One hundred fifty children of 113 fathers with testicular tumour treated from 1979 on the National Institute of Oncology, Budapest, were studied. Three groups were formed on the basis of the time of conception; 69 children were born before the illness of the fathers, 40 during the 12 pretreatment months, and 41 during or after combined chemotherapy. One hundred fifty control children underwent tonsillectomy/appendectomy, but were otherwise healthy. They were matched according to age, sex, and place of inhabitance with index children. Family anamnesis, perinatal, and gestational data were listed; thereafter, physical, laboratory, immunological, and, if required, radiological examinations were made. No difference was detectable in the somatic and psychiatric status of the three groups, and development was well balanced, corresponding to age. Protocols of the combined chemotherapy applied, and the incidence of anomalies, abnormalities, malignancies, and other diseases was recorded. Incidence was similar in all three groups. Incidence of congenital malformations was not increased in children conceived before and after therapy; however, a complex congenital abnormality, an atrial septal defect with horseshoe kidney, occurred in one young girl, conceived after the end of her father's treatment. The interval between conception and the end of therapy was established in the case of children conceived either during or after therapy. This was shorter in the case of healthy children; the number of healthy children conceived during cytostatic treatment was also remarkable. Further detailed analysis of data and individual evaluation of case reports are recommended.