Introduction Quality of health care contributes to poor physical health outcomes for people with mental health and substance use conditions (MHSUC). AIM This study investigated experiences of people with MHSUC who sought help for a physical health condition in primary healthcare services, examining quality of care attributes. Methods An online survey of adults currently or recently accessing services for MHSUC was fielded in 2022. Respondents were recruited nationally through mental health, addiction and lived experience networks and social media. The attributes of service quality assessed were relationships (respect and being listened to), discrimination due to MHSUC, and diagnostic overshadowing (MHSUC diagnosis distracted from physical health care). Results Respondents who had used primary care services were included (n = 335). The majority of respondents reported both being treated with respect (81%) and being listened to (79%) always or most of the time. A minority of respondents reported diagnostic overshadowing (20%) or discrimination due to MHSUC (10%). People with four or more diagnoses or a diagnosis of bipolar disorder or schizophrenia had significantly worse experiences across all quality measures. Those with a diagnosis of substance use disorders had worse experiences for diagnostic overshadowing. Māori had worse experiences for respect and diagnostic overshadowing. Conclusions Although many respondents reported good experiences in primary care, this was not the case for everyone. Quality of care was affected by type and number of diagnoses and the person's ethnicity. Interventions to reduce stigma and diagnostic overshadowing for people with MHSUC are needed in primary care services in New Zealand.