There are many unexplained differences in the rates at which general practitioners make referrals to other medical specialists. We investigated 5082 referrals from 141 general practitioners to dermatologists in Ringkøbing county in Denmark. As an expression of the referral rate to dermatologists an index of referral to dermatologists was estimated for every general practitioner. The index of referral to dermatologists was the number of referrals to the dermatologists per 1000 patients per year, including children, standardized for age and sex to the average population in Ringkabing County. The following six variables were evaluated in relation to the referral index: 1) Distance to the dermatologists, 2) number of doctors per practice, 3) number of consultations per general practitioner per year, 4) number of patients registered, 5) number of consultations per 1000 patients per year standardized for age and sex, and 6) number of supplementary procedures per consultation. Stepwise multiple linear regression analysis was used. The study showed that the referral index to dermatologists fell both with distance to the dermatologist and with the number of supplementary procedures per consultation. No correlation was found between the referral index and the four other variables studied.