In order to determine the incidence and clinical characteristics of acute intermittent porphyria (AIP) a retrospective study was done in Hospital Arzobispo Loayza of Lima for the period 1983-1994. Of 16 patients with that diagnosis, 14 ones (13 female and one male) entered to the study because of their clinical pictures and a positive Watson Schwartz' test. All were Hispanics from Lima. The average age was 24 yr old. The average for delay of diagnosis was 7 days and for hospitalization was 24 days. There was 1.8 AIP attacks by patient. Only 3 patients (21.4%) had familial history of AIP. The most frequent exacerbating factors were infections (52%), menses (20%) and drugs (16%). The main findings were:abdominal pain (100%), hyporexia (100%), nausea and vomit (84%) and dark urine (80%); hyporeflexia (52%); tachycardia (100%), fever (44%), arterial hypertension (40%) and abdominal distention (40%); anemia (52%), hyponatremia (48%), elevated ESR (40%) and increased activity of SGOT and SGPT (36%). It was found an annual incidence of 1.05 AIP cases and 1.9 attacks by 1000 discharged patients from the Medicine wards. Besides, we found similar clinical characteristics in our patients as it has been reported in the medical literature.