This study extends research into insight by examining its relationship to a variety of demographic, clinical, neurocognitive, and psychosocial variables among a broad diagnostic sample of 211 adults with serious mental illness. Participants completed a full battery of instruments measuring these variables. Results support a relationship between ratings of poor insight and a psychotic (vs. mood) diagnosis, increased psychiatric symptoms, poorer social skills, and negative medication attitudes. Minorities and those with a substance abuse diagnosis were also more likely to be rated as having poor insight. No relationship was found between level of insight and age, gender, education level, neurocognitive deficits, hospitalization history, size of one's social network, or quality of life measures. Results are discussed in the context of improving the measurement and assessment of insight, conceptualizing interventions aimed at addressing level of insight, and improving outcomes for patients with severe and persistent mental illness. Findings also support a need for continued investigation of how mental illness is understood, experienced, and expressed across diverse groups of people living with mental illness.