Land gastropods were collected at twelve secondary-growth hardwood sites throughout the White Mountains of New Hampshire in 1980 and again in 1996, using the cardboard collection technique advocated by Boag (1982). A comparison of the results showed a 52% decline in gastropod density from 13.9 to 6.6 gastropods/m2 of cardboard over the sixteen year period. Many factors can influence gastropod densities including changes in moisture conditions, vegetation composition, forest age, and dietary calcium levels. They also experience natural fluctuations in population size caused by variations in birth and mortality rates, and the prevalence of disease and predation. After evaluating the influence of each of these factors, I present declines in forest calcium as a result of acidification as the primary cause of the observed decrease in gastropod abundance in the White Mountains. Future monitoring of gastropod populations could be a valuable indicator of the effects acid precipitation has on the forests of the White Mountains.