A high prevalence of mental health diagnoses in adults alongside ongoing shortages of mental health specialists and expansion of the patient-centered medical home have increased the involvement of primary care clinicians in treating mental health concerns. Using nationally representative serial cross-sectional data from the 2006-18 National Ambulatory Medical Care Surveys regarding visits to outpatient primary care physicians by patients ages eighteen and older, we sought to characterize temporal trends in primary care visits addressing a mental health concern. Based on a sample of 109,898 visits representing 3,891,233,060 weighted visits, we found that the proportion of visits that addressed mental health concerns increased from 10.7 percent of visits in 2006-07 to 15.9 percent by 2016 and 2018. Black patients were 40 percent less likely than White patients to have a mental health concern addressed during a primary care visit, and Hispanic patients were 40 percent less likely than non-Hispanic patients to have a mental health concern addressed during a primary care visit. These findings emphasize the need for payment and billing approaches (that is, value-based care models and billing codes for integrated behavioral health) as well as organizational designs and supports (that is, colocated therapy or psychiatry providers, availability of e-consultation, and longer visits) that enable primary care physicians to adequately address mental health needs.