OBJECTIVES: Aldosterone plays an important role in the pathophysiology of congestive heart failure (CHF). Blockade of aldosterone receptors by spironolactone substantially reduces risk of morbidity and mortality among patients with CHF. However, benefits of spironolactone are potentially limited by its treatment compliance and adverse events profile, particularly hyperkalemia and gynecomastia. The purpose of this study was to estimate the use of spironolactone in patients with CHF, the incidence of key adverse events and patients compliance to spironolactone. METHODS: This study was performed using data from the Quebec provincial medical and drug plans (RAMQ). Data on medical and pharmaceutical services from January 2000 to September 2008 were obtained from the RAMQ for patients who had a diagnosis of CHF (ICD-9 codes = 4280-4289) during that period.  Relative incidence of gynecomastia  and hyperkalemia was estimated for users and non users of spironolactone. Treatment adherence was estimated for initial users of spironolactone and compared to adherence with ACE inhibitors, beta-blockers and ARBs. RESULTS: RAMQ data were obtained for a total of 82,018 patients with a diagnosis of CHF. Among these patients, 59.9% used an ACE inhibitor, 59.5% a beta-blocker, 28.4% an ARB. and 12,344 (15.1%) had used spironolactone. Incidence of hyperkalemia (3.3% vs. 1.4%) and of gynecomastia (1.8% vs. 0.7%) was significantly higher among spironolactone users compared to non users (p<0.001). Treatment compliance was significantly lower with spironolactone compared to ACE inhibitors, beta-blockers and ARBs (45.6% vs. 56.1%, 59.7%, 57.0% respectively; p<0.001). Persistence to treatment over a one year period was also lower with spironolactone compared to ACE inhibitors, beta-blockers and ARBs (50.7% vs. 64.5%, 70.4%, 66.3% respectively; p<0.001) CONCLUSIONS: Although the use of spironolactone may be beneficial for patients with CHF, its usefulness is limited by the incidence of adverse events and its relatively poor treatment compliance.