This review was undertaken to record recent progress in understanding and management of this unusual, relatively rare, but potentially fatal disease of trophoblast in the fetal allograft. The generic term "gestational trophoblastic neoplasia" has been introduced to represent the broad spectrum of clinical behaviour. The cytogenetic origin is interestingly diverse and the chromosomal karyotype of the tumour is varied, depending upon the type of antecedent pregnancy. The major contribution to progress in the last decade has come from the accumulation of experience by tumour registries and referral centres. Data from studies of biochemical markers, especially of hCG-beta and more recently, SP1, and their accurate measurement have led to the development of a sensitive method of monitoring the disease during follow-up and treatment. Diagnosis is enhanced by ultrasound examination and treatment by suction aspiration is generally regarded as the safest mode of molar evacuation. Although prophylactic chemotherapy has resulted in reduction in incidence of persistent disease (especially in the "high risk" patient), an alternative and, perhaps more rational method, is close follow-up by hCG-beta levels. A better understanding of the use of chemotherapy and the success in achieving the objectives of early treatment when tumour load is small, and selection of the most effective regimen, on the basis of matching type of treatment to the likelihood of drug response (or resistance), are now extended to consideration of treatment for the resistant tumour or tumour in less accessible sites, such as in the brain. With these advances, reproductive function can safely be preserved in the younger patient, unnecessary drug toxicity avoided, mortality reduced considerably and long-term sequelae of chemotherapy kept at an insignificant level.U