During July 1999, 172 crabs from Ubatuba Bay, São Paulo, Brazil, were examined from 4 families as follows: Portunidae, Arenaeus cribrarius, Callinectes danae, Callinectes ornatus, Charybdis hellerii, Portunus spinimanus, and Portunus spinicarpus; Calappidae, Hepatus pudibundus; Majidae, Libinia ferreirae; Leucosiidae, Persephona mediterranea and Persephona lichtensteinii. One cephaline gregarine symbiont was found in the hindgut of a specimen of Cal. ornatus, and no positively identified, internal and multicelled symbionts were detected. Twenty-one specimens (14.3%) from 7 of the 10 species (all except H. pudibundus, P. mediterranea, and P. lichtensteinii) carried the nemertean worm, Carcinonemertes carcinophila ct. imminuta in either their egg masses or gills. This is the first report of this epibiont from the Ubatuba region. Two specimens of an undescribed polychaete worm were found in the gill of a specimen of L. ferreirae. A stalked barnacle, Octolasmis lowei, was found on the gills of 11 crabs (7.5%). Only 3 crab species (36.6% of Cal. danae, 9.0% of Cal. ornatus, and 7.7% of Po. spinimanus) carried the typical barnacle, Chelonibia patula, on their dorsal carapaces. The percentage of individuals of Cal. danae and Cal. ornatus hosting barnacles (prevalence) as well as the number of barnacles on individual crabs was positively correlated with crab size.