Objective: Many children with pervasive developmental disorders (PDDs) have serious, functionally impairing behavioral problems. We tested whether combined treatment (COMB) with risperidone and parent training (PT) in behavior management is superior to medication alone (MED) in improving severe behavioral problems in children with PDDs. Method: This 24-week, three-site, randomized, parallel-groups clinical trial enrolled 124 children, aged 4 through 13 years, with PDDs, accompanied by frequent tantrums, self-injury, and aggression. The children were randomized 3:2 to COMB (n = 75) or MED (n = 49). The participants received risperidone monotherapy from 0.5 to 3.5 mg/day (with switch to aripiprazole if risperidone was ineffective). Parents in the COMB group (n = 75; 60.5%) received a mean of 10.9 PT sessions. The primary measure of compliance was the Home Situations Questionnaire (HSQ) score. Results: Primary: intent-to-treat random effects regression showed that COMB was superior to MED on HSQ (p = 0.006) effect size at week 24 (d) = 0.34. The HSQ score declined from 4.31 (plus or minus 1.67) to 1.23 (plus or minus 1.36) for COMB compared with 4.16 (plus or minus 1.47) to 1.68 (plus or minus 1.36) for MED. Secondary: groups did not differ on Clinical Global Impressions-Improvement scores at endpoint; compared with MED, COMB showed significant reductions on Aberrant Behavior Checklist Irritability (d = 0.48; p = 0.01), Stereotypic Behavior (d = 0.23; p = 0.04), and Hyperactivity/Noncompliance subscales (d = 0.55; p = 0.04). Final risperidone mean dose for MED was 2.26 mg/day (0.071 mg/kg), compared with 1.98 mg/day for COMB (0.066 mg/kg) (p = 0.04). Conclusions: Medication plus PT resulted in greater reduction of serious maladaptive behavior than MED in children with PDDs, with a lower risperidone dose. (Contains 5 tables and 2 figures.)