Completers of four-month Extension Phase protocol who have maintained significantly improved status (decrease greater than 25% in ABC from Protocol I Baseline ratings and CGI of much or very much improved) will be randomized at the end of four months to placebo substitution or risperidone continuation. Group assigned to placebo substitution will undergo weekly blinded reductions of entry dose (dosage at end of Phase I) by 25% per week over three consecutive weeks. After full placebo substitution, placebo group will remain on placebo for total of up to 5 weeks (three-week taper, five-week remaining on placebo). Group assigned to continued active treatment will be maintained on entry dose level for full 8 weeks of Phase II, assuming no behavioral deterioration. Active treatment patients may have dose reduced for treatment emergent effects.