OBJECTIVE: To clarify whether combination treatment with desmopressin (DDAVP) and thiazide was clinically effective in a patient with congenital nephrogenic diabetes insipidus (CNDI), we evaluated the treatment in a 7-year-old boy with CNDI who had demonstrated a partial response to DDAVP. METHOD: Both volume of urine and the presence of nocturia were determined during treatment. RESULT: Neither the usual therapy of a low-salt diet and a thiazide nor intranasal therapy with a large dose of DDAVP was effective. However, combination treatment resulted in a decrease in urinary volume and the disappearance of nocturia. CONCLUSION: DDAVP coupled with thiazide may be useful for CNDI in patients who have shown a partial response to DDAVP. Copyright 2003 S. Karger AG, Basel