Antimony-based medications continue to be the chosen drug for visceral leishmaniasis treatment in most countries. Pentavalent antimony compounds are highly effective but frequently have adverse reactions. Although toxic effects are almost always reversible, some of them can be severe. Clinical and laboratory data of 13 patients who developed severe adverse reactions to meglumine antimoniate in a teaching hospital in southwestern Brazil in 2004-2005 were analysed. Most patients were adults (10/13), mainly at the age of 50 or older (4/13). The main severe adverse reactions were renal failure (eight episodes), pancreatitis (six episodes) and hepatic failure/hepatitis (five episodes). Six patients died in the period; all presented acute renal failure and four presented hepatic failure. Meglumine antimoniate can cause severe reactions, which can lead to death if not promptly identified. Further studies are warrented on the effect of less toxic drugs.