Ascariasis is a neglected tropical disease (NTD) affecting 763 million people worldwide, with nutritional and developmental consequences of chronic childhood infection and severe clinical disease occurring in heavy infections. Reliably estimating the extent of the problem of Ascaris lumbricoides and ascariasis is difficult because of inaccuracies in parasitological diagnosis, the non-specificity of clinical signs, and a paucity of reliable and accurate data. As a consequence, estimating the global distribution and disease burden has been based on informed approximations, using the best available information. This chapter provides an overview of past and current estimates of the global population at risk of and infected with A. lumbricoides. The regional and global burden of ascariasis is estimated by extrapolation from data on the prevalence of infection and a series of epidemiological methods. The Global Burden of Disease (GBD) study uses disability-adjusted life years (DALYs) to measure disease burden, based on an assessment of premature mortality and years lived with disability. The data and methods used to estimate the disease burden of ascariasis in the 1990 GBD study and the 2010 study are compared. Globally, intestinal nematodes are estimated to contribute 5.184 million DALYs in 2010, with ascariasis contributing 1.3148 million, trichuriasis 0.6382 million, and hookworm 3.2311 million. The 2010 study provides estimates for both 1990 and 2010, and these findings indicated that the burden of ascariasis in 2010 is much lower than in 1990, where ascariasis contributed 4.2173 billion DALYs. The use of DALYs to estimate the burden of ascariasis is not without its limitations, however, and fails to capture the broader societal impact of ascariasis and other NTDs or that they disapportionally affect the poorest populations. © 2013 Copyright © 2013 Elsevier Inc. All rights reserved.