PURPOSE: To report results of the Parent's Observations of Social Interactions (POSI) and identify associations between POSI results with referrals for developmental evaluations and autism diagnoses. METHODS: We examined data from electronic health records of POSI-screened children attending 18- and 24-month health supervision visits from July 2018 to July 2022 for POSI screening results and autism diagnoses. Descriptive statistics and regression models were used for analysis. RESULTS: In 6669 POSI-screened children (age at follow-up, 42-107 months), 1065 of 4228 children screened at 18 months (25.2%) and 851 of 4896 children at 24 months (17.4%) screened positive. In 1079 children with positive POSI screenings, 233 children (21%) were referred for developmental evaluation. Autism was diagnosed in 184 of all 6669 children (2.8%). The POSI sensitivity for autism was 66.4% (95% CI 59.2-72.8%) and the positive predictive value was 9.2% (95% CI 7.4-10.6%). A positive POSI increased the likelihood of autism diagnosis at 18 months (adjusted odds ratio, 5.21
95% CI 3.45-7.86) and 24 months (adjusted odds ratio 10.21
95% CI 7.07-14.76). Autism was diagnosed 13 months earlier in children with a positive rather than negative POSI (35.5 vs 48.1 months
P <
0.001). CONCLUSION: The POSI is a sensitive screening instrument for autism with a low positive predictive value (high percentage of false positive screenings), indicating the need for clarification about which children require further evaluation. Screening positive on the POSI was associated with a greater likelihood and earlier diagnosis of children with autism.