Two Italian controlled trials demonstrated that the difference in remission rates obtained with six months of methylprednisolone and chlorambucil (MP+Ch) compared to MP was smaller than MP+Ch versus symptomatic therapy in the treatment of idiopathic membranous nephropathy nephrotic syndrome (NS). A decision analysis was used to compare the three treatment strategies, assuming triple probabilities and costs for MP+Ch complications compared to MP, with no risk for supportive therapy, referring to an average 40-year-old patient and using the quality-adjusted life expectancy year (QALY) as the utility scale. With MP+Ch the difference in expected QALY was 7.2 years compared to supportive therapy, and 2.6 years compared to MP. To offset the longer survival obtained with MP+Ch versus MP, it was assumed that all patients treated with MP+Ch would undergo either fatal (5% vs. 0.3% with MP) or non-fatal complications (95% vs. 15% with MP). This threshold denotes a great stability of the inequality in the expected QALY. Consequently, treatment with MP or with MP+Ch is justified if their side effects are considered to be a suitable trade-off for a five or seven QALY, respectively, longer survival. Only an absurd increase in the death rate with MP+Ch could offset the difference.