The objective of this study was to assess the efficacy and tolerability of low-dose fluvoxamine (1.5 mg/kg/day) in youngsters with pervasive developmental disorders (PDDs). This was a prospective, open-label trial that included 18 subjects with a mean age of 11.3 +/- 3.6 years. Fourteen children (78%) completed the 10-week study. Premature discontinuation due to behavioral activation occurred in three participants. Although there was no response for the group as a whole, eight subjects (including all four females) were considered at least partial responders in intent-to-treat analyses. Neither pubertal status nor serotonin levels predicted clinical response. Fluvoxamine can be beneficial in the treatment of select children and adolescents with PDDs. Gender differences in selective serotonin reuptake inhibitor (SSRI) response warrant further investigation.