Snail shells persist in the environment after death, but we know little about the rate at which shells decompose. Assumptions about the rate of shell decomposition are relevant to conservation biologists who find empty shells or biologists using empty shells to make inferences about assemblages of living individuals. I put shells in 1.6 mm mesh litter bags (excluding macro-grazers) in Delaware and northern Michigan, U.S.A. and monitored shell mass annually for 7 years. Decomposition rates differed among species, but I found no difference in rates at two sites with different habitats. Surprisingly, loss of periostracum had no effect on shell decomposition rate. At the locations and habitats studied, decomposition rate of snails averaged 6.4% per year, excluding shells that broke during the experiment (shell half life = 11.5 years), or 10.2%, including shell breakage (half life = 7.5 years). Half lives would likely be shorter if macro-grazers had access to shells. These results caution us to draw conclusions carefully when including empty shells in inferences about assemblages of living individuals.