To study trends in human immunodeficiency virus (HIV) seroprevalence in blood donors in northern Pakistan.Analysis of annual data from blood transfusion centre.Data records from people who had donated blood at the Armed Forces Institute of Transfusion (AFIT) between 1998 and 2013 were retrieved and analysed.All blood donations were tested for the presence of HIV antibodies using Abbott Inc's AxSYM from 1998 to 2006, and Abbott Inc's Architect 2000i with chemiluminescence microplate immunoassay from 2007 to 2013.Over the 16-year study period, 66 donors tested positive for HIV antibodies out of 626,413 donations (0.01%, i.e. 10 per 100,000 donations). From 1998 to 2006, 16 HIV-positive cases were detected out of 280,245 donations (0.0057%, i.e. 5.7 per 100,000 donations). However, from 2007 to 2013, 50 HIV-positive cases were detected out of 346,168 donations (0.0144%, i.e. 14 per 100,000 donations). The difference in HIV positivity between the two groups was found to be significant (0.0057% vs 0.0144%, χ2 = 10.4, P = 0.008).A gradual and persistent increase in the number of HIV-positive cases among blood donors in northern Pakistan was seen over the study period. The HIV-positive cases reported one or more high-risk activities in the past which predisposed them to HIV infection.