Summary The relationship between history of schistosomiasis and bladder cancer risk was investigated using data from a case-control study conducted between January 1994 and July 1996 in Alexandria, Egypt. Cases were 190 subjects with incident, histologically confirmed invasive cancer of the bladder, and controls were 187 subjects admitted to hospital for acute, non-neoplastic, non-urinary tract conditions. Eighty-six cases (45%) vs 69 controls (37%) reported a history of urinary schistosomiasis. The corresponding multivariate odds ratio (OR) of bladder cancer -after allowance for age, sex, education, smoking, other urinary infections and high-risk occupations -was 1.72 (95% confidence interval (Cl) 1.0-2.9). The ORs were 0.22 (95% Cl 0.1-0.4) for intestinal schistosomiasis and 0.32 (95% Cl 0.1-1.9) for schistosomiasis of other types. The OR for urinary schistosomiasis was higher in subjects who were younger at first diagnosis (OR of 3.3 for <15 years) and in those with a long time since first diagnosis (OR of 3.0 for . 35 years). The ORs were 15.8 for male ever-smokers with a history of urinary schistosomiasis, compared with never-smokers without such a history, and 3.2 for men ever-infected with urinary Schistosoma haematobium and ever-employed in high-risk occupations, compared with those never-infected and with no high-risk occupational history. This study confirms that clinical history of urinary schistosomiasis is significantly, but modestly, associated with increased bladder cancer risk, explaining some 16% of bladder cancer cases in this Egyptian population.Keywords: bladder cancer; epidemiology; schistosomiasis; tobacco Bladder cancer rates in Egypt are the highest in the world, with overall age-standardized (world standard) death certification rates of 10.8 per 100 000 in men and 2.3 per 100 000 in women . In Alexandria, where incidence rates have been available since 1972, bladder cancer incidence was 19.2 per 100 000 in men and 3.6 per 100 000 in women. Bladder cancer was the commonest of all cancers in men (17.5%), and more than twice as common as lung cancer (Bedwani et al, 1993).This substantial excess has been generally attributed to a high prevalence of Schistosoma haematobium infection (urinary schistosomiasis). An association between bladder cancer, particularly squamous cell cancer (Lucas, 1982), and infection with S. haematobium has long been suggested by clinical observations as well as by analytical and descriptive epidemiology. The relation has been explained through chronic irritation of the urothelium, altered metabolism with elevated urinary levels of carcinogenic metabolites and N-nitroso compounds and/or elevated urinary levels of Pglucuronidase (Matanoski and Elliott, 1981; WHO, 1994; Badawi et al, 1995).It has been estimated that the prevalence of schistosomal infection was over 20% for women and over 40% for men during the