IMPORTANCE: The prevalence of psychological distress among mothers of children with autism spectrum disorder (ASD) suggests a need for interventions that address parental mental health during the critical period after the child's autism diagnosis when parents are learning to navigate the complex system of autism services. OBJECTIVE: To investigate whether a brief cognitive behavioral intervention, problem-solving education (PSE), decreases parenting stress and maternal depressive symptoms during the period immediately following a child's diagnosis of ASD. DESIGN, SETTING, AND PARTICIPANTS: A randomized clinical trial compared 6 sessions of PSE with usual care. Settings included an autism clinic and 6 community-based early intervention programs that primarily serve low-income families. Participants were mothers of 122 young children (mean age, 34 months) who recently received a diagnosis of ASD. Among mothers assessed for eligibility, 17.0% declined participation. We report outcomes after 3 months of follow-up (immediate postdiagnosis period). INTERVENTIONS: Problem-solving education is a brief, cognitive intervention delivered in six 30-minute individualized sessions by existing staff (early intervention programs) or research staff without formal mental health training (autism clinic). MAIN OUTCOMES AND MEASURES: Primary outcomes were parental stress and maternal depressive symptoms. RESULTS: Fifty-nine mothers were randomized to receive PSE and 63 to receive usual care. The follow-up rate was 91.0%. Most intervention mothers (78.0%) received the full PSE course. At the 3-month follow-up assessment, PSE mothers were significantly less likely than those serving as controls to have clinically significant parental stress (3.8% vs 29.3%; adjusted relative risk [aRR], 0.17; 95% CI, 0.04 to 0.65). For depressive symptoms, the risk reduction in clinically significant symptoms did not reach statistical significance (5.7% vs 22.4%; aRR, 0.33; 95% CI, 0.10 to 1.08); however, the reduction in mean depressive symptoms was statistically significant (Quick Inventory of Depressive Symptomatology score, 4.6 with PSE vs 6.9 with usual care; adjusted mean difference, -1.67; 95% CI, -3.17 to -0.18). CONCLUSIONS AND RELEVANCE: The positive effects of PSE in reducing parenting stress and depressive symptoms during the critical postdiagnosis period, when parents are asked to navigate a complex service delivery system, suggest that it may have a place in clinical practice. Further work will monitor these families for a total of 9 months to determine the trajectory of outcomes. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01021384.