Port Lockroy, situated on the Antarctic Peninsula, is one of the most visited tourist sites in Antarctica. The effects of visitor disturbance on the breeding performance of gentoo penguins (Pygoscelis papua) at Goudier Island, Port Lockroy was investigated during the austral summer of 1996/1997 by comparing pairs in treatment areas (visited by 35–55 tourists every 1–2 days) and control colonies (not visited by tourists). There were no differences between the two groups in the proportion of birds that laid, in hatching success or the proportion of single-chick broods. Pairs in treatment colonies laid a higher proportion of single-egg clutches, but this was related to colony location and unusually high snow accumulation. Most treatment colonies were situated on low-lying ground or in the lee of buildings, and probably had more late layers at the initial census. Only 11% of tourist visits had occurred by laying, making human disturbance an unlikely explanation for the higher proportion of single-egg clutches. Nests monitored in a disturbed colony and a control colony showed no differences in chick mass or survival up to 20 days of age. The overall breeding success, based on counts of creched birds, was similar to other southern populations of gentoo penguins, after correcting for mortality between creching and fledging. Historical data from Goudier Island indicate that the colony established itself in 1985 and has rapidly increased in size since then. The neighbouring colony at Alice Creek, which has been regularly visited by tourists for at least a decade, has also shown a population increase, although this expansion has been at a slower rate. We conclude that disturbance from tourist visits is unlikely to have been a major determinant of gentoo population change at Port Lockroy.