The present study examined the associations between networks of social relationships and psychological well-being among mothers of adolescents and adults with autism (n = 352) over a 12-year period of time. A structural equation modeling approach was used to delineate the relative impacts of network size and relationship diversity on maternal mental health, and to assess whether such effects are bidirectional. Mothers with more diverse relationships experienced reductions in depression and anxiety symptoms over time, and the psychological benefits of diversity remained after adjusting for network size. Results also suggest bidirectional links between network size, diversity, and maternal mental health. Research and clinical implications are discussed.