We studied the distribution and abundance of finless porpoises (Neophocaena phocaenoides) in Hong Kong and adjacent waters of China’s Guangdong Province between September 1995 and November 2000. Vessel (50,194 km) and helicopter (2,696 km) surveys were used to assess distribution patterns, and estimates of abundance were calculated using line transect methods. Acoustic detection data from a towed porpoise click detector (POD) were used to make an estimate of the trackline detection probability [g(0)] for ship surveys, and surface and dive time data were used for correcting helicopter survey estimates. Porpoises occurred in Hong Kong and adjacent waters year-round, but showed evidence of seasonal movements, with porpoises largely vacating most of Hong Kong’s southwestern waters in summer and autumn. Seasonal changes in overall abundance were also evident. The peak season within Hong Kong waters was spring, in which an estimated 152 porpoises inhabited territorial waters. The peak estimates for all areas combined (217 porpoises in spring and summer) can be viewed as a minimum estimate of the size of the local population. Examination of potential violations of line transect assumptions indicate that the techniques used were well-suited, with no evidence of serious biases. However, because the distribution clearly extends beyond the study area and the exact range limits are unknown, further work is needed to assess overall population size.