Objective To investigate contraceptive use among HIV-positive women in Ha long city and Cam Pha town of Quang Ninh, a Northern province of Vietnam. Methods Cross-sectional questionnaire study among HIV-positive women identified through the district HIV/AIDS register. Information on socioeconomic characteristics and contraceptive use before and after HIV diagnosis was obtained through structured questionnaires. Chi-square testing was used to assess whether the included women differed from the target population in terms of age. Crude Odds ratios (ORs) were calculated to show the association between contraceptive use and the women's socioeconomic characteristics. Logistic regression analyses were applied to adjust for possible confounding. The women's contraceptive use before HIV testing and after HIV testing was described and compared by Chi-square testing, and the association between post-test counselling and the women's use of condom was assessed by ORs. Results Of the 351 participants, 63% stated they had used contraception before HIV diagnosis and 89% stated they had used contraception after HIV diagnosis. Forty six per cent of the women had been using either the pill or an intrauterine device (IUD) before the diagnosis whereas the same applied for only 8% of the women after diagnosis. Thirty-nine per cent stated they had been using condom before HIV diagnosis whereas 87% stated condom use after HIV diagnosis. Condom use was more common among women who had received post-test counselling (OR 3.03, 95% CI 1.03-8.90). Conclusions A change of contraceptive methods from IUD and oral contraception before HIV diagnosis to condom use after HIV diagnosis was observed. The women's use of condoms after HIV diagnosis was associated with having received post-test counselling.