Polyuria is defined as the passage of large volumes of diluted urine secondary to an abnormality of urine concentration. This disorder can result either from deficient secretion of vasopressin (cranial diabetes insipidus), or from renal resistance to vasopressin (nephrogenic diabetes insipidus), primary polydipsia, osmotic diuresis, electrolytic disorders or drugs. Suspicion of impaired renal concentration ability can be confirmed by a fluid deprivation test. The administration of exogenous vasopressin allows to clarify the pathogenetic mechanism. Once the mechanism responsible for polyuria has been clarified it is mandatory to search for underlying causes. Treatment of polyuria should be causal, if its origin is known, and/or symptomatic in order to prevent severe dehydration. Symptomatic treatment of cranial diabetes insipidus consists of administering exogenous vasopressin. Salt restriction associated to a combined administration of hydrochlorothiazide/amiloride or hydrochlorothiazide/indomethacin can reduce urine output by 20 to 50% in case of nephrogenic diabetes insipidus. Pollakiuria is defined as a daytime urinary frequency. It can be isolated or may be a manifestation of lower urinary tract infections, bladder instability, nephrolithiasis or concentrated acidic urines. Detailed history and physical examination represent major clues to diagnostic. Therapy of pollakiuria can be causal or symptomatic using anticholinergic drugs or reeducation in case of bladder instability. Nocturia is characterized by voluntary nocturnal micturitions secondary to conditions inducing impaired renal concentration ability, or to heart failure.