Data from a multiphase schizoaffective disorder study (NCT01193153) were used to examine the effects of paliperidone palmitate once-monthly (PP1M) by subjects' illness duration, defined as recent onset (5 years since first psychiatric diagnosis; n = 206) and chronic illness (>5 years; n = 461). Symptom and functioning scores, as measured during open-label PP1M acute and stabilization treatment phases, improved in both subpopulations, with greater improvements in recent onset than chronic illness subjects (p 0.022). Relapse rates, examined during the double-blind, placebo-controlled phase, were higher with placebo than PP1M: 30.0% vs. 10.2% (p = 0.014; hazard ratio [HR]: 2.8; 95% confidence interval [CI]: 1.11-7.12; p = 0.029) in the recent onset subpopulation and 35.5% vs. 18.1% (p = 0.001; HR: 2.38; 95% CI: 1.37-4.12; p = 0.002) in the chronic illness subpopulation. Growing evidence in the treatment of schizophrenia and schizoaffective disorder supports early intervention with long-acting antipsychotics.