Encrusted cystitis is characterized by chronic inflammation of the bladder with encrustation of the mucosa, induced by urea-splitting bacterial infection. However, encrusted cystitis in itself is not well known. We report a case of encrusted cystitis causing postrenal failure. An 81-year-old man with pneumonia complained of pollakisuria, micturition pain, and gross hematuria. Bladder calculi were found, and transurethral lithotripsy was performed. However, because his symptoms did not improve, he was referred to our hospital. His urine pH was 8.5, and urine culture grew Corynebacterium and Proteus. Computerized tomography and cystoscopy revealed bladder "encrustation," caused by bladder wall calcification, and bilateral hydronephrosis. Hence, he was diagnosed with postrenal failure resulting from encrusted cystitis. Immediate bilateral nephrostomy was constructed, with continuous bladder perfusion with an acid solution for acidification of his urine, followed by intravenous administration of ceftriaxone. After 2 weeks of treatment, the calcification disappeared and his bladder mucosa was normalized. The postrenal failure also improved and thus the nephrostomy tubes were removed. Encrusted cystitis is curable by prompt treatment with acidification of urine. Therefore, precise diagnosis and therapy are critical.