Sixty-five (38 male and 27 female) preschool children (mean age=5 years 1 month) completed measures of peers' trustworthiness (promise keeping and secret keeping). Teachers rated the preschool children's inhibitory control, trustworthiness, and preschool adjustment. Structural Equation Modeling (SEM) yielded support for the hypothesized model. The expected positive paths were found from (1) gender to preschool adjustment and inhibitory control, (2) age to peer-reported trustworthiness, (3) peer-reported trustworthiness to preschool adjustment, (4) inhibitory control to peer-reported trustworthiness, and (5) inhibitory control to preschool adjustment. The findings confirmed the hypothesized development of trustworthiness with age and girls' advantage over boys in inhibitory control and preschool adjustment. The findings supported the hypotheses that trustworthiness is associated with preschool adjustment and mediates, in part, the relation between inhibitory control and preschool adjustment.