We determined whether patients with serious mental illness (SMI) were less likely than non-SMI to self-report having a medical condition that was recorded in their medical record. We included all patients from the VA National Psychosis Registry diagnosed with SMI and a random sample of non-SMI patients in fiscal year 1999 who completed the Large Health Survey of Veteran Enrollees (N = 35,837). Among patients with diagnoses for any of 11 conditions recorded in administrative data, we evaluated whether patients reported having that same condition in the survey, using multivariable logistic regression and generalized estimating equations. Among patients diagnosed with a given condition, those with SMI were less likely to report being told by providers that they had seven of the 11 conditions examined: heart disease (OR = 0.68, p < 0.001), arthritis (OR = 0.79, p < 0.001), cancer (OR = 0.69, p < 0.001), diabetes (OR = 0.79, p < 0.001), back pain (OR = 0.81, p < 0.001), congestive heart failure (OR = 0.71, p < 0.001), and hypertension (OR = 0.77, p < 0.001). Patients with SMI were less aware of co-occurring medical conditions.