Background: Migrant populations are at high risk of Human Immuno Deficiency Virus infection (HIV) and Acquired Immunodeficiency Syndrome (AIDS). Studies of HIV/AIDS knowledge, attitudes and practices among fishermen in developing countries have shown gaps in knowledge and fear of contagion with ambivalent attitudes towards HIV/AIDS and inconsistent universal precautions adherence. The aim of this study was to determine the knowledge, attitude and practices regarding HIV/AIDS among adult fishermen in a coastal area of Karachi, Pakistan. Methods. Community based cross sectional study was conducted among fishermen in coastal area of Karachi from June to September 2012. A total of 297 adult fishermen were selected by using simple random sampling technique from different sectors of coastal village. Data were collected using a structured validated questionnaire. The frequency distribution of both dependent and independent variables were worked out. Comparisons of knowledge, attitude and practices regarding HIV/AIDS by socio-demographic characteristics were made using logistic regression. Results: Out of 297 fishermen, majority had in-appropriate knowledge (93.6%), negative attitude (75.8%) and less adherent sexual practices (91.6%). In univariate analysis, lower education and higher income were significantly associated (OR 2.25, 95% CI, 1.11, 4.55), (OR = 3.04 CI 1.03-9.02, p value 0.04) with negative attitude and un-safe practices towards HIV/AIDS respectively, whereas no significant association of socio-economic characteristics with knowledge, attitude and practices were observed in multivariate analysis. Conclusions: This study suggests that fishermen had very poor knowledge, negative attitudes towards HIV and AIDS and had unsafe sexual practices which suggest that they lack the basic understanding of HIV/AIDS infection. Extensive health education campaign should be provided to the vulnerable sections of the society for the control of HIV/AIDS.