Growing evidence has highlighted the importance of motor proficiency in relation to psychosocial outcomes including self-perceived competence in various domains, perceived social support, and emotional areas such as anxiety and depression. The Environmental Stress Hypothesis-elaborated (Cairney, Rigoli, & Piek, 2013) is a proposed theoretical framework for understanding these relationships and recent studies have begun examining parts of this model using child and adolescent populations. However, the extent to which the relationships between these areas exist, persist or change during early adulthood is currently unclear. The current study aimed to investigate the Environmental Stress Hypothesis in a sample of 95 young adults aged 18-30. years and examined the mediating role of physical self-worth and perceived social support in the relationship between motor proficiency and internalising symptoms. The McCarron Assessment of Neuromuscular Development (McCarron, 1997) was used to assess motor proficiency, the Depression Anxiety Stress Scale (Lovibond & Lovibond, 1995) provided a measure of internalising symptoms, and the Physical Self Perceptions Profile (Fox & Corbin, 1989) and the Multidimensional Scale of Perceived Social Support (Zimet, Dahlem, Zimet, & Farley, 1988) were used to investigate the possible mediating role of physical self-worth and perceived social support respectively. Potential confounding variables such as age, gender and BMI were also considered in the analysis. Structural Equation Modelling revealed that perceived social support mediated the relationship between motor proficiency and internalising symptoms, whereas, the mediating role of physical self-worth was non-significant. The current results provide support for part of the model pathways as described in the Environmental Stress Hypothesis and suggest an important relationship between motor proficiency and psychosocial outcomes in young adults. Specifically, the results support previous literature regarding the significant role of perceived social support for mental well-being and suggest that an intervention that considers social support may also indirectly influence mental health outcomes in young adults who experience movement difficulties. © 2016 Elsevier B.V.