In their everyday practice, primary-care physicians are often asked to refer patients to a specialist without a prior appointment in primary care. Such referrals are problematic, and one might suspect that patients who make such requests are more likely to have mental comorbidities predisposing them toward higher utilization of health-care services. In a cross-sectional study, 307 patients of 13 primary-care practices who requested referral to a specialist without a prior appointment in primary care were given a Patient Health Questionnaire (PHQ) containing questions that related to depression, anxiety, panic disorder, and somatoform disorder (independent variables). Further information was obtained about these patients' primary-care contacts, referrals, and days taken off from work with a medical excuse over the course of one year (dependent variables). A regression model was used to compare these patients with 977 other primary-care patients. The groups of patients who did and did not request specialist referral without a primary-care appointment did not differ to any statistically significant extent with respect to mental comorbidity. In the overall group, somatoform disorder was found to be associated with a high rate of primary-care contacts (odds ratio [OR] 2.4, 95% confidence interval [CI] 1.4-4.3). High rates of referral were strongly correlated (percentage of variance explained, R²) with depression (OR 2.1, 95% CI 1.1-4.0; R² = 35.3%), anxiety (OR 4.1, 95% CI 1.8-9.6; R² = 34.5%), panic disorder (OR 5.9, 95% CI 2.1-16.4; R² = 34.3%), and somatoform disorder (OR 2.2, 95% CI 1.2-4.0; R² = 34.6%). Taking a long time off from work with a medical excuse was correlated with depression (OR 2.5, 95% CI 1.2-4.8), anxiety (OR 4.2, 95% CI 1.7-10.5), and somatoform disorder (OR 2.2, 95% CI 1.2-4.2). Mental comorbidity contributes to the increased utilization of health-care services. This should be borne in mind whenever a patient requests many referrals to specialists (either with or without a prior appointment in primary care). It is important to identify "doctor-hopping" patients so that the causes of their behavior can be recognized, discussed, and properly treated.