In December 2004, a questionnaire was sent to 44 institutions that maintained Gorillas Gorilla gorilla. Twenty-six institutions replied (59% response rate) providing information about 91 hand-reared Gorillas in the European Endangered Species Programme (EEP) population. Using other sources, such as the international studbook and EEP reports, data on 63.54 (♂.♀) Gorillas that had been hand reared between 1980 and 2004 were analysed. Over this period, 23 (43%) ♀♀ and 15 (24%) ♂♂ bred successfully. However, when the numbers used to make the analyses were corrected by removing Gorillas (1) that had not yet reached full sexual maturity (>12 years for ♂♂ and >10 years for ♀♀) and (2) were not maintained in breeding groups, and including three ♀♀ that bred before they were 10 years of age, the percentages for breeding success are 65% for ♂♂ and 61% for ♀♀. These results demonstrate that hand-reared individuals contribute to the increase in the EEP Gorilla population observed over the past 25 years.