The current study investigated maternal determinants of mental health service use, namely, individual child therapy, among preadolescent children diagnosed with ADHD. The Behavioral Model of Health Care Utilization (Andersen, 2008) was used as a theoretical framework for the study. Data from the last three rounds of ECLS-K dataset were employed to test a longitudinal model using Bayesian analysis. Socio-demographic variables and maternal mental health were tested as exogenous variables and mother-child relationship variables, discipline variables, and perceived maternal concern about child’s overall behavior and child’s emotional symptoms were tested as intervening variables. Results showed that only maternal mental health remained in the model as an exogenous variable. The effect of mental health on child therapy was mediated by maternal aggravation and maternal concern about overall behavior in one path and by maternal concern about emotional symptoms in another path, suggesting that maternal mental health needs to be considered when attempting to understand help-seeking determinants. Both concern variables were found to have large direct effects on child therapy. The results of the current study showed the importance of maternal mental health and the importance of determinants related to mother-child relationship in a mother’s decision to seek therapy for a child.