Summary Mortality up to 1 January 1983 has been studied in 14,106 patients with ankylosing spondylitis given a single course of X-ray treatment during For leukaemia there was a threefold increase in mortality that is also likely to have been due to the radiotherapy. The relative risk was at its highest between 2.5 and 4.9 years after the treatment and then declined, but the increase did not disappear completely, and the risk was still nearly twice that of the general population more than 25.0 years after treatment. There was some evidence that the risks of acute myeloid, acute lymphatic, and chronic myeloid leukaemia were all increased, but no evidence of any increase in chronic lymphatic leukaemia. The relative risk appeared to be greatest for acute myeloid leukaemia.For colon cancer, which is associated with spondylitis through a common association with ulcerative colitis, mortality was increased by 30%.For non-neoplastic conditions there was a 51% increase in mortality that was likely to be associated with the disease itself rather than its treatment. (Court Brown & Doll, 1965) and related the incidence of leukaemia to the dose received. These analyses included many patients who had been treated with X-rays for their spondylitis more than once and it was not clear whether the increase that continued for many years should be attributed to the first or subsequent courses. When Smith & Doll (1978;1982) reported on the follow-up of the patients to 1970, they avoided this difficulty by restricting the analyses to patients who had received only a single course of treatment. Their analyses showed that, when the mortality of the spondylitic patients was compared with that of the general population, the relative risk of leukaemia was at a maximum 3-5 years after treatment and subsequently declined. For other cancers of sites judged to be heavily irradiated, the relative risk was at a maximum 9-11 years after treatment and then declined to less than one after 24 years. Only a small proportion of patients had been followed beyond 20 years, however, and the decreasing trend in relative risk for these other cancers more than 11 years after treatment was not statistically significant. We have, therefore, sought to find out how long the increased mortality from leukaemia and other cancers persisted following X-ray treatment by extending the follow-up of patients who received only a single course of treatment by a further 13 years and have related the increased mortality to organ dose. We report here only the data for total and organ specific mortality and have deferred discussion of the complex relationship with dose to a later report. Material and methodsStudy population andfollow-up

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Summary The distribution of mortality from 11 causes of death (lymphoid leukaemia, other Reports of an increased incidence of leukaemia in young people in the vicinity of certain nuclear installations have caused concern about the possible effect on communities that live near other such installations. The extent and localisation of the increase near Sellafield leaves no doubt about its reality (Gardner & Winter, 1984) but it is unclear how far many of the other reports represent selection of high rates that are bound to occur by chance, while low rates are neglected. To check this possibility the evidence relating to all the installations in the country needs to be examined. This, however, is not easy to do as the reorganisation of local government in 1974 altered the boundaries of most administrative units and made it difficult to obtain relevant figures for each area of interest over a long enough period.In England and Wales the Office of Population Censuses and Surveys (OPCS) overcame this difficulty by using the pre-1974 local authority areas (LAAs) and allocating the cancer registrations and deaths that had been reported since 1974 to the old areas . In that study, LAAs with more than a third of their population within 10 miles of an installation were' compared with control LAAs that were chosen to be more distant from the installations, but of similar population size, urban/rural status and, as far as possible, within the same standard region. The results suported the idea that in recent years the mortality from leukaemia, and especially lymphoid leukaemia, in young people tended to be relatively high in areas close to installations that began operations before 1955, but showed that in adults mortality from all cancers, considered as a group, tended to be relatively low . Some of the relatively high rates around nuclear installations were, however, difficult to assess, as the main reason for them was unusually low rates in the control LAAs.We have, therefore, tackled the problem in another way. Like OPCS we have limited ourselves to England and Wales Correspondence: P.J. Cook-Mozaffari.

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Recent developments in statistics have produced powerful methods that facilitate the analysis of longitudinal studies. These methods are illustrated by an analysis of a longitudinal study of blood pressure in children. The results of the study show a clear tendency for blood pressure to increase with age, and Asian children tend to have lower blood pressures than their Caucasian counterparts of the same age. There is evidence to support the hypothesis that blood pressures track.