Studies on the biology of the franciscana dolphin (Pontoporia blainvillei) in the Río Negro Estuary (RNE), Patagonia, Argentina, were carried out from 2002 to 2011. Information about group size, group dispersion and behaviour was collected from the coast and by boat, using scanning and focal animal/group sampling methodology. Group size varied from 1 to 5 dolphins (
= 1.69; standard deviation (SD) = 0.74; N = 121), 2 being the most frequent value (46.28%; N = 56). Group dispersion varied from 0 to 10 dolphin length (DL) (
= 1.4; SD = 0.75; N = 51), 0 DL (54.9%; N = 28) being the most frequent value. Behaviour of travelling, feeding, milling and resting were recorded, with a higher frequency of animals travelling (36.58%; N = 45). Calves were observed in spring and summer (N = 10). 13 stranded individuals were reported and 3 of them were collected from gillnets. Data presented herein indicate year-round presence of franciscana as well as the RNE being the southernmost breeding and feeding site reported to date. The establishment of the proposed natural reserve by the Governments of Río Negro and Buenos Aires provinces and continued long-term studies are urgently recommended.