Long-term outcome of acute pyelonephritis (AP) in adults is unknown. We evaluated the frequency of renal damage 10-20 years after hospitalization for AP in adult women and the utility of technetium Tc 99m-labeled dimercaptosuccinic acid (Tc 99m-DMSA) scanning for detection of renal scars; 63 of 203 women hospitalized with AP during 1982-1992 were included in the study. Tc 99m-DMSA scanning detected renal scarring in 29 women (46%). Multivariate analysis showed that pregnancy and hypoalbuminemia (albumin level, <3.2 g/dL) at hospitalization were independent risk factors for subsequent development of renal scars. At follow-up, hypertension was observed in approximately one-fifth of patients, regardless of renal scarring status. Four women with scars had a glomerular filtration rate of < or =75 mL/min; none of them developed severe renal impairment. In conclusion, the risk of developing renal scarring after AP in adult women is high. However, clinically relevant renal damage is rare 10-20 years after AP. Tc 99m-DMSA scanning is useful for detecting renal scars in adults but is not routinely needed in practice.