The authors describe the design and implementation of a large multiethnic c
ohort established to study diet and cancer in the United States. They detai
l the source of the subjects, sample size, questionnaire development, pilot
work. and approaches to future analyses. The cohort consists of 215,251 ad
ult men and women (age 45-75 years at baseline) living in Hawaii and in Cal
ifornia (primarily Los Angeles County) with the following ethnic distributi
on: African-American (16.3%), Latino (22.0%), Japanese-American (26.4%), Na
tive Hawaiian (6.5%), White (22.9%), and other ancestry (5.8%). From 1993 t
o 1996, participants entered the cohort by completing a 26-page, self-admin
istered mail questionnaire that elicited a quantitative food frequency hist
ory, along with demographic and other information. Response rates ranged fr
om 20% in Latinos to 49% in Japanese-Americans. As expected, both within an
d among ethnic groups, the questionnaire data show substantial variations i
n dietary intakes (nutrients as well as foods) and in the distributions of
non-dietary risk factors (including smoking, alcohol consumption, obesity,
and physical activity). When compared with corresponding ethnic-specific ca
ncer incidence rates, the findings provide tentative support for several cu
rrent dietary hypotheses. As sufficient numbers of cancer cases are identif
ied through surveillance of the cohort, dietary and other hypotheses will b
e tested in prospective analyses.