We examined abundance, growth, and secondary production of Ptychophallus tumimanus (Rathbun) (Brachyura: Pseudothelphusidae) in riffles of Quebrada Marilin and Rio Tempisquito, two low-order streams (mean discharge = 0.018 and 0.30 m³ s^-1; mean water temperature = 21.5°C) in northwestern Costa Rica. Density and biomass were estimated from 10 modified Surber samples (0.24 m² per sample) collected monthly between 1996 and 2007. Growth rate was estimated from crabs reared in laboratory streams that continuously receive stream water from Tempisquito. Crab density was almost 2X higher in Marilin versus Tempisquito (9.5 and 4.9 crabs m^-2, respectively). However, crab biomass was slightly less in Marilin than in Tempisquito (698 and 778 mg AFDM m^-2) because small crabs were more common in Marilin whereas large crabs were more common in Tempisquito. Growth rate was 0.005-0.011 d^-1, depending on body size. Average annual crab production in Marilin (2083 mg AFDM m^-2 yr^-1) and Tempisquito (1923 mg AFDM m^-2 yr^-1) were similar. The low annual P/B (2.5-3.0) reflects the relatively slow growth rate and long lifespan (maximum=4 years) that we observed in the laboratory.