BACKGROUND: Recent health reform laws might accelerate high-deductible health plan (HDHP) growth. The impact of HDHPs on long-term colorectal cancer screening rates and low socioeconomic status (SES) members is unknown. METHODS: We studied colorectal cancer screening rates among 1306 Health Maintenance Organization (HMO) members for 1 year before and 2 years after an employer-mandated switch to HDHPs, compared with 1306 propensity score-matched controls who remained in HMOs by employer choice. HDHP members had full coverage of fecal occult blood testing (FOBT) but colonoscopy, flexible sigmoidoscopy, and double-contrast barium enema were subject to $500 to $2000 annual deductibles. HMO members had full coverage of these tests. We used generalized estimating equations to adjust screening rates for member characteristics. We stratified analyses by SES. RESULTS: Overall colorectal cancer screening rates in the HDHP group relative to the control group trended down from baseline to the first and second follow-up years [ratios of change, 0.88, (95% confidence interval, 0.73 to 1.06) and 0.83, (0.69 to 1.00), respectively]. Low SES HDHP members experienced a statistically significant relative decrease in colonoscopy in both follow-up years [0.65, (0.48 to 0.88) and 0.59, (0.42 to 0.84), respectively] and a trend toward increased FOBT [1.26, (0.92 to 1.72) and 1.30, (0.95 to 1.77), respectively] to maintain stable overall colorectal cancer screening rates [1.01, (0.77 to 1.32) and 0.93, (0.71 to 1.22), respectively]. High SES members experienced less pronounced decrease in colonoscopy [0.89, (0.67 to 1.18) and 0.87, (0.62 to 1.21), respectively] but FOBT rates did not increase [0.83, (0.62 to 1.11 and 0.81), (0.60 to 1.11), respectively]. CONCLUSIONS: Switching to a HDHP was associated with a downward trend in overall colorectal cancer screening rates after 2 years. Low SES HDHP members maintained stable rates, but substituted FOBT for colonoscopy and other tests now more widely recommended. Further research should investigate whether such reduced adherence to screening guidelines adversely affects health outcomes.