Introduction: Sex workers (SW) represent the population exposed to extremely high risk of HIV (HIV Human Immunodeficiency Virus) and other sexually transmitted infections. Poor socioeconomic conditions in the country, insufficient education, high unemployment and other factors lead to an increase in prostitution, which represents a high risk for the spread of HIV and other sexually transmitted diseases. Aim of the study: The aim of this research was to evaluate the prevalence of HIV/ sexually transmitted infections among SW in Bosnia and Herzegovina as well as to examine knowledge, attitudes and behaviour relating to HIV/sexually transmitted infections. The results were compared with the results obtained in researches conducted in 2008 and 2010. Material and Methods: Research was performed in 2012 as a bio-behavioral study that covered 199 sex workers in five cities of Bosnia and Herzegovina. Interviewing was done voluntarily, anonymously and confidentially, and after informed consent and councelling, a biological material (blood) for laboratory testing on HIV, hepatitis b, hepatitis c and syphilis was taken. The research shows the presence of risk behaviour among SW, mostly related to frequent change of partners and frequent unprotected sexual intercourses. Results: Only one third of respondents (36,7%) use condom during every sexual intercourse with a client, and 13% use it with a steady partner.A sexual intercourse after effects of consumption of alcohol-87,9% of respondents and of drugs-36,7% of respondents. Although there is a risk behaviour, only 11,1% think that the risk of HIV/sexually transmitted infections is high, but 12,6% think that there is no risk. Sex workers are 13,5 times more exposed to HIV infection than all the other women aged 1549. Results of laboratory testing indicate a low level of HIV/sexually transmitted infections among sex workers in Bosnia and Herzegovina. Conclusion: Although there is a relative progress in prevention of HIV/sexually transmitted infections among sex workers and more frequent testing on HIV/sexually transmitted infections comparing to earlier periods, these things are insufficient for the maintenance of a low level of infection. Further research at certain time intervals among this population would enable monitoring time trends of HIV epidemic in Bosnia and Herzegovina and would become a basis for the development of preventable programmes.