Initial classifications of 1009 testicular tumours were reviewed as part of a population based survey of all testicular neoplasms in Victoria, Australia, between 1950 and 1978. All reviews were made by one of two pathologists at the Peter MacCallum Cancer Institute, using the system of the British Testicular Tumour Panel. Accuracy of diagnosis varied markedly over the time period and with pathological category. Seven cases were initially designated malignancies but were determined to be non-malignant conditions upon review. In each decade, review reduced the proportion of seminomas and increased the proportion of non-seminoma germ cell tumours (NSGCT) and non germ cell tumours. Reclassification resulted in changed age specific incidences of seminoma and NSGCT, most noticeably in 1950-59. Trends in age standardised incidence of seminoma and NSGCT were not affected by reclassification although the values were. The trend in age standardised incidence of non germ cell tumours was affected by reclassification. The implications of the changes in classification for epidemiological studies and clinical management are discussed.