In the present study a cancer risk assessment of occupational exposure to cyclophosphamide (CP), a genotoxic carcinogenic antineoplastic agent, was carried out following two approaches based on ( 1) data from an animal study and ( 2) data on primary and secondary tumors in CP-treated patients Data on the urinary excretion of CP in health care workers were used to estimate the uptake of CP, which ranged from 3.6 to 18 g/day Based on data from an animal study, cancer risks were calculated for a health care worker with a body weight of 70 kg and a working period of 40 years, 200 days a year (linear extrapolation) The lifetime risks ( 70 years) of urinary bladder cancer in men and leukemias in men and women were found to be nearly the same and ranged from 95 to 600 per million. Based on the patient studies, cancer risks were calculated by multiplication of the 10-year cumulative incidence per gram of CP in patients by the estimated mean total uptake in health care workers over 10 years, 200 days a year The risk of leukemias in women over 10 years ranged from 17 to 100 per million using the secondary tumor data (linear extrapolation) Comparable results were obtained for the risk of urinary bladder tumors and leukemias in men and women when primary tumor data were used Thus, on an annual basis, cancer risks obtained from both the animal and the patient study were nearly the same and ranged from about 1 4 to 10 per million In The Netherlands it is proposed that, for workers, a cancer risk per compound