We present here a case of a 9-year-old boy with bilateral anterior uveitis and an extremely elevated urinary β2-microglobulin level (25,400 μg/l). The normal range for urinary excretion of β2-microglobulin is 0-300 μg/l. In patients with tubulointerstitial nephritis and uveitis syndrome (TINU), elevations typically range from 1,260 to 5,160 μg/l. Renal biopsy was pursued, and significant granulomatous interstitial nephritis consistent with sarcoidosis was identified. Systemic immune modulation was required for control of ocular inflammation. This case highlights the importance of urinary β2-microglobulin testing in the pediatric patient uveitis population, and additionally the need to pursue kidney biopsy in the presence of extreme elevations in urinary β2-microglobulin to differentiate between TINU and sarcoidosis.