Background: Scarce data exist concerning dermatological consultations within departments of internal medicine. To date, no survey has been carried out in Switzerland to elucidate this issue. The aim of this study was to analyze the spectrum of skin diseases internists are confronted with and to study their diagnostic accuracy in cutaneous diseases. In addition, we wanted to evaluate the motivation for dermatologists to cooperate closely with internists. Patients and Methods: The study included patients with dermatological problems treated at the Department of Internal Medicine at the Kantonsspital Aarau, Switzerland. All patients had been referred to the Department of Dermatology for examination between 1999 and 2001. Patient data were analyzed demographically, by referral modus, diagnoses and therapy. To evaluate the knowledge of internists and dermatologists in cutaneous medicine, 15 clinical slides of common dermatoses with a patient history were shown and asked for diagnostic suggestions to 32 internists of the Kantonsspital Aarau and to 13 dermatologists of the University Hospital Basel, Switzerland. Results: 1,290 patients were referred to the Department of Dermatology. 1,737 dermatological diagnoses were made including 348 different dermatoses. Eczema was the single most common diagnosis (12.6%), followed by actinic and bowenoid precancerosis (6.2%), drug eruption (4.2%), verrucae (4%) and mycosis (3.8%). The top ten diagnoses accounted for 41.7% of all skin-related diagnoses. Infection-related dermatoses were most common (20.5%) followed by different types of eczema (12.6%), malignant cutaneous tumors and malignant visceral conditions (11.2%). Local therapy was prescribed in 64.2% and systemic therapy in 22.6% of the patients. 15.9% did not receive specific therapy because the consultation request was only a diagnostic one. 146 skin biopsies were performed (11.3%). Systemic diseases with cutaneous manifestations accounted for 15.7%. In general, these conditions were not commonly seen by dermatologists in daily practice. The internists recognized 51.1% of the cutaneous manifestations during examination and 49% when presented with slides. Conclusions: Internists are confronted with a different spectrum of cutaneous diseases compared with dermatologists. Due to the broad spectrum of skin diseases, it is a challenging task for internists to recognize dermatoses. Our study elucidates that patients, internists and dermatologists may profit from a close cooperation.