Purpose: The purpose of this study was to assess the disclosure of HIV-positive status and its associated factors to sexual partners among patients attending antiretroviral therapy (ART) clinic follow-up at Mekelle Hospital, Tigray, Ethiopia. Patients and methods: An institution-based cross-sectional study was conducted at Mekelle hospital. Samples of 324 individuals were selected by using systematic random sampling techniques from July 1 until July 30, 2013. The data were collected by trained data collectors through a pretested semi-structured questionnaire. The collected data were cleaned, coded, entered, and analyzed using SPSS version 16.0 Windows program. Descriptive statistics and binary and multivariable regression analysis with 95% confidence interval was carried out and P-value less than 0.05 used to determine the significant association. Results: A total of 324 people on ART care follow-up were interviewed with 100% response rate. The overall HIV status disclosure to sexual partner was 57.4%. Among those who disclosed their HIV status, 58% of them told their partner after 1 month after diagnosis. The study showed that there is significant association between knowing HIV status of sexual partner (adjusted odds ratio [AOR] = 16.69, 95% CI: 5.4, 51.65), duration of HIV-related care follow-up (AOR = 5.48, 95% CI = 2.17, 13.80), and discussion before HIV testing (AOR = 4.33, 95% CI = 1.43, 13.08), with HIV-positive status disclosure to sexual partner. Conclusion: An HIV-positive status disclosure to a sexual partner in this study was lower than what was reported in other studies in Ethiopia. The duration of HIV-related care followup, knowing partner's HIV status, and prior discussion were the main factors that affected the practice of HIV-positive status disclosure to their sexual partners.