Chlamydia trachomatis infection in college students has not undergone a detailed large-scale evaluation. The authors undertook a cross-sectional study of 4,086 students enrolled on the campuses of California State University, Sacramento, and 3 local community colleges from fall 2000 through spring 2002. They used an outreach screening model to determine the presence of infection by testing urine for chlamydial DNA by polymerase chain reaction. Participants completed demographic and behavioral risk questionnaires and a chlamydia knowledge assessment. Overall, 3.4% of participants tested positive for infection. Screening of male and female students was evenly distributed and incidence rates for males (3.03%) and females (3.78%) were similar Variables associated with significantly increased risk were younger than 25 years, ethnicity other than White, more than one sexual partner in the preceding year or a new partner in the preceding 2 months, and current symptoms. Innovative outreach programs to screen a majority of at-risk college students should be developed.