In a nation-wide survey among Danish doctors, the compliance and reasons for non-compliance with universal precautions (UP) and the associated circumstances of mucocutaneous blood exposure (MCE) were studied. Of 9384 questionnaires, 6256 (67%) were returned and 6005 were eligible for analysis. Only 35% complied with the basic principles of UP. Compliance with protective barrier use in surgical versus non-surgical specialties was: Gloves 63.0% and 23.4%, masks 55.2% and 17.6% and protective eyewear 11.5% and 4.0% respectively. Common given reasons for non-compliance were: "Interferes with working skills", "forget", "wear spectacles", "not available", "too much trouble to get" or "gloves do not fit". Of 741 MCE described in detail, an estimated 84-98% were potentially preventable if appropriate barriers had been worn. More than half of MCE were preventable by two interventions only: Compulsory use of protective eyewear during operations and of gloves during insertion of peripheral i.v.-catheters. In conclusion compliance with UP is unacceptably low and the majority of MCE were potentially preventable if appropriate barriers had been worn.