This study aimed to establish how dentists' knowledge, opinion and behaviour about cross-infection control were related and how they were affected by their ages, gender and the sizes of the practices in which they worked. In 1990/91 all general dental practitioners in the North Western Health Region of England were asked to complete a questionnaire about cross-infection control; 917 (75%) did so. Responses from all single-handed and one dentist selected randomly from each group practice were analysed (n = 546). The score to measure behaviour was based on guidelines on cross-infection control issued by the British Dental Association and this was correlated with scores for knowledge and opinion. The more knowledgeable not only tended to hold favourable opinions about the guidelines but also to practise them. Younger dentists were more knowledgeable about cross-infection control measures than older and more likely to wear gloves. Irrespective of age, all female dentists were more likely to wear gloves than their male colleagues. Single-handed dentists were less willing to treat carriers of HIV and HBV. Although 65% thought that recommended control procedures are feasible, 43% considered them prohibitively expensive.