Introduction: The HIV/AIDS is still an important problem for global health, with a complex and dynamic epidemiology over time. Objective: To determine the trend on the temporal variation of baseline CD4+ T lymphocyte count in adult's patients diagnosed with HIV at a social security hospital in Lima, Peru. Methods: Descriptive study based on secondary data from adult's patients diagnosed with HIV during the period 1999-2012 in a Peruvian social security hospital, taking into consideration the socio-pathological variables of the patients and trend graphs. Results: 70% of the patients evaluated in this period were men and the median age was 34 years old. There was an increase in the trend of the temporal variation of the baseline CD4+ T lymphocyte count at the moment of diagnosis, and a decrease in the number of patients diagnosed for each year. There were no significant changes in the trends, according to the age groups; but taking into account the sexual orientation, there was a rise in heterosexual and bisexual populations, and a downtrend in the group of men who have sex with men (MSM). Conclusions: We report the favorable trend of the CD4 + T lymphocyte count at the moment of diagnosis in a Peruvian social security hospital, being similar to other realities worldwide, which may allow to continue strengthening preventive programs, especially for the groups that currently show a higher frequency of HIV/AIDS.