<b>Objective: </b>To compare the immune status duringthree years of patients diagnosed with HIV/AIDS who were treated at the San Juan de Dios Hospital. <b>&nbsp;</b> <b>Materials and Methods: </b>Retrospective, descriptive study of the new cases of HIV/AIDS, older than14 years of age, in 2003, 2006 and 2009 at the HIV Outpatient Clinic of the San Juan de Dios Hospital, Costa Rica, according to data in the clinical records. To evaluate the immune status the CD4 + T lymphocytes count at moment of HIV diagnosis was used, establishing as late diagnosis &lt;200 cells. For the analysis, an estimate of the frequency and strength of association between variables was performed. <b>&nbsp;</b> <b>Results: </b>From the282 cases studied, 46.8% of them were at an advanced stage of the illness. Considering all cases, late diagnosis was more frequent in men (54%) than in women (26%) (p&lt;0.05) and in heterosexual men (57%) than in men who have sex with with men (50%) (p&lt;0.05). In regard to age, there is an increase in risk proportional to the increase in age. It was observed that the percentage of late-diagnosis patients has increased throughout the years herein studied. Even though a decrease in the group of patients who come late for the start of the ART was observed, this decrease is due to an increase in late diagnosis and not because of an increase in timely diagnosis. <b>&nbsp;</b> <b>Conclusions: </b>Late diagnosis of HIV infection represents a public health problem in the geographical area covered by the services of the San Juan de Dios Hospital. It is necessary to develop strategies that allow the improvement of the resolving capacity of the primary and secondary levels of attention in order to achieve HIV diagnosis in a timely manner. In the geographical area covered by the San Juan de Dios Hospital, the populations with a greater risk of late diagnosis are heterosexual men between the ages of 25 and 64

HIV; AIDS; CD4-positive T lymphocytes; late diagnosis; immunodeficiency