Growth parameters of 93 Pontoporia blainvillei and 84 Sotalia fluviatilis accidentally captured in gillnets or stranded along the sea coast of northern Rio de Janeiro State, Brazil (2137–2225S) were analysed (1989–96). Data of length-at-age was fitted by nonlinear Gompertz model. Growth parameters estimated for P. blainvillei were: sexual dimorphism in body length significant only to four years, so, length range of 0–3 years not showed growth differentiated; asymptotic length of 117.1 cm for males and 144.7 cm for females; length at birth of 71.0 cm; prenatal growth rate of 0.25 cm/day; birth occur in all seasons; males and females attain sexual maturity at two years, 115.0 cm and at three years, 130.0 cm, respectively. S. fluviatilis presented non sexual dimorphism in body length; asymptotic length of 191.7 cm for males and females; length at birth of 106.0 cm; prenatal growth rate of 0.31 cm/day; birth occur from spring to autumn, with a peak during autumn; males and females attain sexual maturity at six years, with 180.0 cm for male and 160.0 cm for females. The results of the present study suggest that there are alterations in the reproductive investment in P. blainvillei. Probably, this species varies its growth strategies along its distribution. S. fluviatilis showed patterns similar to those observed for other populations of this species.