Social Security has had great success in reducing poverty, on average, among the elderly. Today, the elderly poverty rate is less than one-third the 35 percent rate seen in 1960. Social Security also protects people from inflation and other risks (as we think it should). The success of any program, however, cannot be judged solely by how well that program succeeds on average. To assess Social Securitys marginal success, a good measure is how much each additional dollar spent improves the lot of the population it serves. Here, we describe three pieces of evidence suggesting that Social Securitys ability to meet one of its most fundamental tenets - alleviating old-age poverty - has hit several roadblocks.