Since 1985, partner notification has been part of Swedish policy to prevent the spread of human immunodeficiency virus (HIV) infection. Potentially infected partners of a newly diagnosed seropositive patient are notified either by the index patient or by the physician and referred for counselling. The efficacy of this strategy was assessed over 18 months in 1989-90. 365 HIV-seropositive index patients (91% of the 403 patients diagnosed in Sweden during the study period) reported 564 sexual or needle-sharing contacts. 390 contacts were located and counselled and HIV test results are known for 350 of them. In 53 of the 350 cases, previously unknown seropositivity was diagnosed. Partner notification for HIV should be viewed as a strategy to offer counselling and testing to a high-prevalence group of people. In a country where general HIV prevalence is low, the strategy is cost-effective for location and counselling of unknowingly seropositive individuals.