The diagnosis of renal vein thrombosis is rarely entertained in infants beyond the first months of life, owing largely to statements that the majority of cases occur in the neonatal period. This paper is based on a clinically suspected and successfully operated-on case of renal vein thrombosis in a one-year-old girl. This is the second case reported with survival in the second year of life. In 1953, Mills and Owen1 reported their case, in an 18-month-old girl, with the following comment: "With the exception of Kobernick et al., we have not found any record of the condition occurring in the second year of life." It is our purpose to review the available literature with reference to the age incidence of renal vein thrombosis. During the course of the search of the literature, we also became interested in the incidence of unilateral and bilateral involvement in published series, and the present review includes this aspect of the problem.Report of a Case A one-year-old white girl was admitted on Dec. 21, 1956, with the chief complaint of fever, irrita¬ bility, and an episode of vomiting of 12 hours' duration. The patient had previously been hos¬ pitalized because of aseptic meningitis and had been discharged from the hospital a week prior to this admission. Physical Examination.-Temperature, 103 F ; pulse rate, 160; respirations, 28. Height, 81 cm.; head circumference, 45 cm. ; chest, 50 cm. ; abdo¬ men, 48 cm. The patient was a well-nourished child with grunting respirations. The skin showed a generalized erythema and a diaper rash. There was injection of the pharynx and left ear drum. The neck was negative. There was slight dullness at the right base, and breath sounds were diminished over this area. No rales were heard. The ab¬ domen was soft. No masses were noted, and there was no enlargement of liver, spleen, or kid¬ neys. Extremities were normal, and neurological examination was negative.Laboratory Studies.-Urinalysis : yellow, acid, with albumin 3+, ketones 2+, RBC 5-7, WBC 7.Hemoglobin was 5 gm. ; WBC, 32,600, with a marked shift to the left. NPN was 23 mg/100 cc. ; fasting blood sugar, 120 mg/100 cc. ; CO», 15.5 mEq. per liter; chloride, 117 mEq. per liter; potas¬ sium, 5 mEq. per liter, and sodium, 137 mEq. per liter. Throat culture showed /3-hemolytic strep¬ tococci. Nasopharyngeal culture showed /3-hemolytic streptococci. Blood culture revealed no growth. Urine culture yielded Escherichia coli. Lumbar puncture yielded clear fluid with a total protein of 20 mg/100 cc. ; sugar, 80 mg/100 cc, and chlorides, 783 mg/100 cc. Chest x-ray revealed a pneumonitis at the right base.Course in Hospital.-At the time of admission the clinical impression was acute pharyngitis, otitis media, and possible right lower lobe pneumonitis. Penicillin and streptomycin were started ; the tem¬ perature gradually declined but did not reach normal, rising again on the sixth hospital day. Lumbar puncture was repeated but was again normal. The urine was yellow and acid, with albumin 2+ and sugar 2+. There were numerous red blood cells...