Purpose: Research concerned with the relationship between volunteer activity and psychological well-being has typically reported higher levels of well-being among older adult volunteers relative to nonvolunteers. However, few studies have examined nonlinear associations between frequency of volunteer activity and well-being. We examined nonlinear associations between hours spent volunteering and psychological well-being, controlling for employment status, partner status, physical health, and education. We also investigated associations between different domains of volunteer activity and well-being, along with the possible moderating effects of gender on these relationships. Design and Methods: We used data from the PATH Through Life Project, a population-based study of Australian adults. Participants consisted of 2,136 older adults aged 64 to 68. Results: Nonlinear associations between hours spent volunteering and psychological well-being were evident, with these associations characterized by inverted U shapes, with nonvolunteers and those volunteering at high levels producing lower well-being scores relative to those volunteering at moderate levels. Few associations between specific domains of volunteer activity and well-being were evident, and no notable gender interactions emerged. Implications: The results point toward optimal frequency of engagement in volunteer activity for psychological well-being as being bounded by upper and lower levels, outside of which benefits to well-being diminish.