The growth of Palaemon longirostris H. Milne Edwards, 1837, was studied in Mira River and estuary, SW Portugal, from October 1990 to September 1991. Size was measured as carapace length (CL), total body length (TL), and weight as wet weight (W). Females grew to larger size than males. Carapace length-frequency was used to determine the von Bertalanffy growth equation: L(t) = 11.68 (1 − e^{−0.62(t 0.49)}) for males and L(t) = 16.32 (1 − e^{−0.51(t 1.42)}) for females. The Munro's growth performance index (ϕ) was lower in males (1.927) than in females (2.133). Relationships between size measurements and weight were described with regression equations. Significant sex-specific variation was found in the slopes of the allometric relationships. Female carapace grew faster than total body length and weight, and the opposite was observed for males. In TL–W relationships, the weight increases faster than total body length in females and slower in males.