We report 13 patients with 16 episodes of acute lobar nephronia diagnosed in a prospective study that was conducted among 210 hospitalized children with urinary tract infection. In 30 episodes of urinary tract infection, a hypoechogenic or hyperechogenic lesion was found. Twenty patients underwent computed tomography, and in 16 of them acute lobar nephronia was diagnosed. Evolution to renal abscess occurred in 25%. Prolonged intravenous antibiotic treatment was sufficient in all cases.