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Background: The aim of this study was to compare use of references in responses from Scandinavian drug information centres (DICs). Methods: Six different fictitious drug-related queries were sent to each of seven Scandinavian DICs. The six queries concerned adverse effects, pharmacokinetics, pregnancy, complementary medicine, polypharmacy, and breast feeding. References in the responses were categorised into five types of drug information sources: primary (original studies), secondary (reviews), tertiary (drug monographs, handbooks, etc.), DIC database, or personal communication. Results: Two hundred and forty-four references were used in the 42 responses. The mean number of references varied from 3.0 to 10.6 for the six queries. The largest difference between centres with regard to number of references used (range 1–17) was found for the query on complementary medicine. In total, 124 references (50.8%) were tertiary, and only 10 of the 42 responses (23.8%) did not have any tertiary references included. Complementary medicine, breast feeding, and pregnancy were query types associated with relatively frequent use of primary references. Use of DIC database was not uncommon, but personal communications were seldom used. Conclusions: Scandinavian DICs differ substantially in number and type of references to identical drug-related queries. Tertiary sources are mainly preferred irrespective of type of query.