This paper presents baseline data on nurses' knowledge of and attitudes to HIV/AIDS in three countries: Finland, Estonia and Lithuania. The prevalence of HIV/AIDS is steadily increasing in Finland, Estonia and Lithuania. At the same time, labour mobility and also nursing mobility between these countries increases. Previous international studies have shown that lack of knowledge and negative attitudes continue to exist. A total of 681 registered nurses from one Finnish (n = 322), one Estonian (n = 191) and one Lithuanian (n = 168) hospital were surveyed in spring 2006. The questionnaire was originally developed by Held in 1993 and modified for this study. The questionnaire has three scales: demographic and other background variable, nurses' knowledge related to HIV/AIDS, and nurses' attitudes towards people with HIV/AIDS and towards the disease itself. Across the whole sample respondents showed average levels of HIV/AIDS knowledge and attitudes towards people with HIV/AIDS. Years of work experience correlated negatively with the knowledge and attitude levels. A significant correlation was found between the level of knowledge and attitudes. Significant differences were found between countries, Finnish nurses showing the highest knowledge levels and most positive attitudes towards patients with HIV/AIDS. Factors positively influencing levels of knowledge and attitudes were education, previous experience of providing care to HIV/AIDS patient or knowing someone with the infection, and willingness to provide care to HIV/AIDS patients. Supplementary education is needed to strengthen nurses' knowledge. It is important to recognize that there might be differences in knowledge and attitudes between neighbour countries. This needs to be taken into account when planning education for degrees and for further nursing education.