Lithium is a well established therapeutic agent in the treatment of uni- and bipolar affective disorders. Angiotensin-converting enzyme (ACE) inhibitors are the most frequently used class of drugs in the treatment of cardiovascular diseases. Combination therapy with both may be considered in clinical practice on occurrence of arterial hypertension after years of successful lithium therapy, yet an increased risk of lithium intoxication in combination with ACE inhibitors has been described and thus the combination has been warned against. We describe three cases in which enalapril, lisinopril or ramipril was combined with lithium. Either additional co-medication with hydrochlorothiazide or dehydration rather than co-medication with ACE inhibitors could be identified as necessary factors for lithium intoxication. These cases suggest that a combination of lithium with ACE inhibitors is possible when sufficient hydration is ensured and a combination with hydrochlorothiazide is avoided. Lithium concentration should be controlled on a regular level.