OBJECTIVEThis study aimed to ascertain the serum levels of selectins (E, L, P) and platelet-endothelial adhesion molecule-1 (PECAM-1) in preschool children with autism spectrum disorder (ASD) and to establish a comparison with the levels observed in healthy controls.METHODSThe study included 34 children aged 2-7 years diagnosed with ASD (ASD group) and 34 randomly selected healthy children matched for age and sex to the ASD group. The children were free of any genetic or physical disease, clinically active infection, or medication use. The sociodemographic data form was completed by all parents. The Childhood Autism Rating Scale (CARS) and the Autism Behavior Checklist (ABC) were administered to the patient group, and the Aberrant Behavior Checklist (AbBC) was completed by the families of all children. Serum selectin (E, L, P) and PECAM-1 levels were measured using enzyme-linked immunosorbent assay (ELISA) kits.RESULTSThe results showed that the levels of both L-selectin (p = 0.007) and PECAM-1 (p = 0.019) were significantly lower in the ASD group than in the control group. No significant difference was observed between the groups concerning E-selectin and P-selectin levels (p > 0.05). It was observed that P-selectin variables were statistically significant in predicting the presence of ASD (p = 0.019). A remarkable inverse correlation was found between the AbBC irritability subscale score and L-selectin (r = -0.296, p = 0.014) and PECAM-1 (r = -0.276, p = 0. 023); the AbBC Lethargy-Social Withdrawal subscale score and E-Selectin (r = -0.239, p = 0.049), L-Selectin (r = -0.297, p = 0.014) and PECAM-1 (r = -0.264, p = 0.029); L-Selectin levels and the AbBC stereotypic behavior subscale (r = -0.248, p = 0.042). No statistically significant relationship was observed between selectins (E, L, P) and PECAM-1 levels and CARS scale, ABC subscale or total scores and age variables (p > 0.05).CONCLUSIONSThese study results suggest that L-selectin, P-selectin and PECAM-1 may play a role in the pathophysiology of ASD.