At the present time, there are no uniform standards for the duration of non-rodent chronic toxicity studies. The European Union (EU) requires a 6-month non-rodent study. In Japan, a 6-month study is sufficient for most, but not all, compounds. The U.S. Food and Drug Administration (FDA) maintains its standard duration of 12 months for non-rodents, with 6-month studies accepted for some clinical indications on a case-by-case basis. To achieve harmonization on the duration of non-rodent toxicity studies, each member regulatory region (EU, U.S., and Japan) of the International Conference on Harmonization (ICH) collected non-rodent studies with significant new toxicological findings that had occurred after 6 months. An ICH expert working group was organized that included representatives from the regulatory authorities of each ICH region, to jointly review all available case studies for the purpose of arriving at a consensus on the best duration time for non-rodent toxicity studies. Eighteen case studies were identified and evaluated (16 original cases plus 2 additional FDA cases); most of the toxicities identified fell into the following categories: (1) toxicities identified at 6 months; (2) toxicities observed at 12 months, which were absent or considered isolated and not noteworthy findings at 6 months; (3) drug-related deaths or morbidity that occurred between 6 and 12 months, with a pattern of toxicity that permitted the interpolation of findings to an intermediate interval between 6 and 12 months; and (4) a shift in the dose response for toxicity with increasing duration of drug exposure. Of the 18 cases evaluated, 11 supported a study-duration of 9-12 months, 4 supported a duration of 12 months, and the 3 remaining cases indicated that a 6-month study would be adequate. The working group concluded that there was sufficient evidence to support a harmonized 9-month duration for non-rodent toxicity studies, which would be applicable for most categories of pharmaceuticals.