Objective: To analyze the characteristics of newly reported HIV/AIDS cases in medical institutions in Tianjin from 2005 to 2017 and provide evidence for the improvement of AIDS prevention and treatment in medical institutions. Methods: The data of the newly reported cases of HIV/AIDS in medical institutions in Tianjin from 2005 to 2017 were analyzed. Meanwhile a retrospective survey was conducted on the source department of medical institutions and the main disease for treatment of HIV/AIDS cases. Results: A total of 3 035 HIV/AIDS cases were reported in medical institutions in Tianjin from 2005 to 2017 with an annual increase of 24.8%, among these cases, 49.2% (1 343/2 728) were reported from inpatients and 50.8% (1 385/2 728) were reported from outpatients. There was an increasing trend in the HIV positive detection rate in STD outpatients from 2011 to 2017 (χ(2)=18.469, P=0.005). The counts of the first CD(4)(+) T cell counts (CD(4)) (χ(2)=17.189, P=0.000) among the cases from inpatients and outpatients and the proportions of deaths in the year when the cases were found differed (χ(2)=61.198, P=0.000), the differences were significant. And the statistically significant differences in the counts of the first CD(4) (χ(2)=16.751, P=0.000) and the proportions of deaths in the year when the cases were found (χ(2)=18.926, P=0.000) existed among the cases in grade Ⅲ hospitals and in grade Ⅱ hospitals; meanwhile the differences in the counts of the first CD(4) (χ(2)=37.620, P=0.000) and the proportions of deaths in the year when the cases was found ( χ(2)=95.489, P=0.000) among the cases from different departments were significant. Conclusion: The timeliness of HIV/AIDS case reporting by outpatient departments was better in medical institutions in Tianjin, and the case reporting in grade Ⅱ hospitals were more timely than in grade Ⅲ hospitals; so it is suggested to provide active HIV test in key departments of medical institutions for the better HIV/AIDS prevention and control in Tianjin.