Part of a cost-effectiveness study of in-vitro fertilization was the evaluation of the medical results of this fertility treatment. Data were prospectively collected from >3000 IVF treatments in five Dutch hospitals during a 2-year period. The average 'take-at-least-one-healthy-baby-home-rate' per started treatment was 10% (the average clinical pregnancy rate per embryo transfer was 20%). After more P/F treatments, about one in three to four couples were successful. Differences in results were mainly caused by patient characteristics, the treatment episode and the treating hospital. These differences remained in a multivariate logistic regression analysis.