Adrenal insufficiency is the most common endocrine disorder affecting HIV infected subjects and it is associated with increased morbidity and mortality. In spite of this, there is paucity of published reports on adrenal insufficiency in children infected with HIV in African countries. This study was conducted to determine the adrenocortical functions of HIV infected children seen at the OAUTHC, Ile-Ife. This prospective study was carried out on consecutive HIV infected children aged less than 18years. Apparently healthy HIV uninfected children, age- and sex-matched with subjects were recruited as controls. Demographic data and physical examination findings were collected for subjects and controls. Blood samples were analyzed for serum cortisol levels, Na+, K+, random blood sugar and CD4 count. Blood samples were collected before and 30 minutes after intravenous injection of 1µg of Synacthen (ACTH) for ELISA analysis of basal and stimulated cortisol levels respectively. The cut-off value for basal and stimulated serum cortisol was set at ≥ 7µg/dl and ≥ 18 µg/dl respectively. A total of 40 subjects and 40 controls aged between 2 to 16 years were studied. The mean ± SD of basal serum cortisol level was 11∙5 ± 5∙6 µg/dl in subjects; this was significantly lower than the mean ± SD of 15∙6 ± 3.8 µg/dl in controls (t = 3∙742, p = 0∙000). Eight (20.0%) of the subjects had basal serum cortisol levels less than 7µg/dl and none of the controls had basal serum cortisol less than 7 µg/dl (χ2=8.889, df =1, p = 0∙003). The mean ± SD of stimulated serum cortisol levels was 18∙4 ± 6∙7 µg/dl in the subjects; this was significantly lower than the mean ± SD of 21∙2 ± 4∙2 µg/dl in the controls (t = 2∙196, p = 0∙031). Twenty-two (55.0%) of the subjects compared with 7 (17∙5%) of the controls had stimulated serum cortisol < 18 µg/dl. This difference was statistically significant (χ2 =12.170, df =1, p = 0∙000). The prevalence of adrenal insufficiency in the subjects was 20.0% for basal serum cortisol while it was 55.0% for stimulated serum cortisol.