Guidelines recommend regular screening for colorectal cancer (CRC). We examined the effects of chronic comorbidities on periodic CRC testing. Using linked healthcare databases from Ontario, Canada, we assembled a population-based cohort of 50–74-year olds overdue for guideline-recommended CRC screening between April 1, 2004 and March 31, 2016. We implemented multivariable recurrent events models to determine the association between comorbidities and the rate of becoming up-to-date with periodic CRC tests. The cohort included 4,642,422 individuals. CRC testing rates were significantly lower in persons with renal disease on dialysis (hazard ratio, HR 0.66, 95% confidence interval, CI 0.63 to 0.68), heart failure (HR 0.75, CI 0.75 to 0.76), respiratory disease (HR 0.84, CI 0.83 to 0.84), cardiovascular disease (HR 0.85, CI 0.84 to 0.85), diabetes (HR 0.86, 95% CI 0.86 to 0.87) and mental illness (HR 0.88, CI 0.87 to 0.88). There was an inverse association between the number of medical conditions and the rate of CRC testing (5 vs. none: HR 0.30, CI 0.25 to 0.36; 4 vs. none: HR 0.48, CI 0.47 to 0.50; 3 vs. none: HR 0.59, CI 0.58 to 0.60; 2 vs. none: HR 0.72, CI 0.71 to 0.72; 1 vs. none: HR 0.85, CI 0.84 to 0.85). Having both medical and mental comorbidities was associated with lower testing rates than either type of comorbidity alone (HR 0.72, CI 0.71 to 0.72). In summary, chronic comorbidities present a barrier to periodic guideline-recommended CRC testing. Exploration of cancer prevention gaps in these populations is warranted.