Urolithiasis (UL) can present with its classic signs and symptoms, such as flank or abdominal pain and gross hematuria. However, atypical complaints can be more common in younger children. We report here a case of bilateral ureteropelvic junction (UPJ) stones in a 10-month-old boy who only showed nonspecific symptoms at the time of presentation. The initial blood test revealed renal failure (serum creatinine 3.4 mg/dl), hyperkalemia (6.4 mEq/l), hyperphosphoremia (9.4 mEq/l) and mild metabolic acidosis. Medical treatment for electrolyte disorders was started. The ultrasonography revealed impacted stones in both ureteropelvic junctions. A pigtail catheter was placed in each ureter. High urine flow was promptly achieved after the pigtail procedure, and the serum creatinine level dropped quickly from 4.5 to 0.32 mg/dl. Quantitative determination of urinary amino acids by ion exchange chromatography showed high cystine levels of 8.43 mmol/g creatinine. Outpatient follow-up was scheduled every 3 months to monitor patient compliance with potassium citrate. In the first 6 months, the patient underwent three febrile urinary tract infections (UTIs). Since both pigtail catheters were removed, he has been free of UTIs and stones. Our case emphasizes the need for considering UL in infants who complain with unclear signs, because UL can only show nonspecific symptoms in children younger than 1 year old. Since cystinuria can cause loss of renal function due to urinary system obstruction and UTI, an early diagnosis and a close follow-up are the key to achieving the best long-term outcome.