Background <p>Depression and/or posttraumatic stress disorder (PTSD) commonly co-occur with opioid use disorder (OUD), and such co-occurring disorders (COD) are especially common among patients in primary care settings. Therefore, addressing the mental health needs of people with COD in primary care is essential.</p> Methods <p>We compared the characteristics of three groups of patients who screened positive for OUD and depression and/or PTSD: (OUD + depression, OUD + PTSD, and OUD + depression + PTSD) and examined how membership in these groups was associated with suicidality and treatment. We analyzed cross-sectional baseline survey data from a larger study of collaborative care for COD. 797 adult patients were seen in 17 primary care clinics that provide care for diverse uninsured and underinsured patients in New Mexico and California. Our key independent variable was COD group. Dependent variables were suicidal ideation and behavior; and receipt of treatments for COD 30&#xa0;days prior to baseline.</p> Results <p>The patient group with all three conditions was larger than the other groups with only two disorders (OUD + PTSD (no depression) or OUD + depression (no PTSD). Patients with all three disorders reported more severe OUD, depression, and PTSD symptoms and higher probability of suicidality. Patients with PTSD (with or without depression) were more likely to report receiving medication for OUD and mental health counseling compared to those with no PTSD, and those with OUD, PTSD, and depression were more likely to report receiving medication for mental health problems than those with just two disorders.</p> Conclusions <p>Higher probabilities of suicidality and of receiving mental health treatment among those with all three disorders point to the need for identifying these individuals in primary care.</p> Trials registration <p>Clinicaltrials.gov, Identifiers, Registration Dates: NCT0455989; NCT04559893, September 8, 2020.</p>