Many individuals with a mental illness are not satisfied with their communication with their primary provider. The present study examined the relationship of serious mental illness (SMI), substance use disorder (SUD), and trust for the provider with provider communication. The sample included Veterans Administration (VA) patients throughout the United States who either had a SMI diagnosis (schizophrenia or bipolar disorder) or were in a random sample of non-SMI patients (total N = 8,089). Latent class (LC) modeling identified three classes of provider communication ratings in the sample: very good, good, and poor. In LC regression, poor trust for the provider was associated with a decrease in the likelihood of being in the overy goodo or ogoodo compared to the opooro provider communication ratings group, and the decrease was significantly greater for VA patients with a SMI or SUD diagnosis than those without. Training providers on creating trust is particularly important for those who serve patients with SMI and SUD diagnoses.