Much of the variation in trace metal tissue concentrations in marine invertebrates has been attributed to the variety in individual organism size, age and sex. This study assessed the relationship between total mercury (Hg) concentrations in edible tissue, exoskeleton and viscera with length, weight and gender for 69 samples of crustaceans, Penaeus semisulcatus (n = 30), Thenus orientalis (n = 21) and Portunus pelagicus (n = 18) from the northern part of the Persian Gulf. Significant increase in the Hg level in muscle and viscera (r > 0.65, p < 0.01) with an increase in length and weight for all three species. No relationship was found between the Hg level in exoskeleton and length or weight. Significantly higher Hg levels (p < 0.01) were found in female P. semisulcatus than in males (muscle and viscera), but no gender differences were found for the other two species.