OBJECTIVE: To measure effects on mental and other healthcare expenses of family members of patients with bipolar disorder, schizophrenia, and major depression. METHODS: Using data from a 2-million member healthplan, the authors estimated and compared expenses for mental and other healthcare services per person per month (PPM) of family members of patients with bipolar disorder, schizophrenia, and major depressive disorder with those of controls. Ordinary least squares and logistic regression models were used to estimate differences and identify characteristics affecting healthcare expenses within each group. RESULTS: Living with patients with bipolar disorder, schizophrenia, or major depression increased both mental and other healthcare expenses for family members, compared with controls. Mental and other healthcare expenses increased as follows: bipolar disorder, $8.85/PPM (213%; P<0.0001) and $10.65/PPM (7.4%; P<0.0001); schizophrenia, $4.03/PPM (81%; P<0.0001) and $5.96/PPM (4.2%; P<0.005); major depression, $8.24/PPM (219%; P<0.0001) and $9.46 (6.5%; P<0.0001). Within all three groups, men were less likely to use mental healthcare services (P<0.002), and the likelihood of mental healthcare use increased with illness duration (P<0.005). Within the bipolar and major depression groups, parents and spouses of patients were more likely to use mental healthcare services than children and siblings (P<0.0001), and the likelihood of mental healthcare use increased with illness severity (P<0.0001). Within all three groups, other healthcare expenses were higher for parents and spouses of patients (P<0.0001-P<0.01) and with longer illness duration (P<0.0001-P<0.0005); men had lower expenses (P<0.0001-P<0.05). Within the bipolar and major depression groups, other healthcare expenses were higher for family members of older patients (P<0.0001-P<0.003). CONCLUSION: Living with a person with serious mental illness significantly increases healthcare expenses of family members, especially for mental healthcare. Family members of patients with bipolar and major depressive disorders have higher healthcare expenses than those of patients with schizophrenia among commercially insured persons.