The aim of the study was to elucidate possible sex differences in knowledge, competence and attitudes behind decision-making on cobalamin-associated problems (vitamin B(12)). The study was conducted by postal questionnaires to Swedish physicians in 1996-98. The participants were recruited by random sampling of general practitioners (1996, 1998), and a total sampling of geriatricians (1998). The overall response rate was 71%. The study group comprised 480 female physicians and 526 male physicians. The responses to 24 statements in the questionnaire were measured by means of visual analogue scales. Group differences were evaluated by medians and shapes of distributions. The female doctors appeared to value patient-related symptoms and signs more than male doctors. Conversely, male doctors relied on laboratory tests more than female doctors. As reflected by questionnaire answers, female doctors appeared to be more informed than male doctors on cobalamin-associated clinical problems. Group differences between the sexes were marginal from a numerical point of view. It is suggested that the statistical differences observed should be regarded as negligible until confirmed by further studies.