Acute pyelonephritis (APN) results from bacterial invasion of the renal parenchyma. The aim of this study was to investigate the epidemiological, clinico-biological, therapeutic and evolutionary APN and to identify the risk factors of this renal disease.We conducted a retrospective and descriptive study, over a period of 37 years (1977-2014), including 43 patients with APN, hospitalized in our Department.There were 43 patients with mean age of 36.98 years. The sex ratio M/W was 0.39. The history of our patients was diabetes (16.28%), recurrent urinary tract infection (25.58%), chronic kidney failure (CKF) (46.51%), Renal lithiasis (9.3%), malformative uropathy (9.3%) and immunosuppressive therapy (23.3%). Typical clinical triad (fever, back pain and urinary functional signs) was present in 25 patients (58.14%). The Gram-negative bacilli represented 97.67% of bacteria isolated in urine culture, dominated by Escherchia coli in 83.72% of cases. APN was simple in 19 cases (44.18%) and at risk of complications in 24 cases (55.81%). Thirty-nine patients (90.69%) had non-severe APN. Four patients (9.3%) had severe APN. Complications were found in 30.23% of cases: acute renal failure (ARF) (30.23%), renal abscess (2.33%), septic shock (4.65%). Risk factors for developing ARF were the higher age group to 60 years (p = 0.02) and CKF (p = 0.001). A significant correlation was found between vesicoureteral reflux and recurrent infections (p = 0.01). Five years renal survival was 69%.APN induced ARF is a serious risk for progression to CKF.