Continuous screening is defined as the periodic provision of an opportunity for diagnostic testing to a population of individuals who are asymptomatic and at increased risk for disease. If screening is offered periodically irrespective of response to an earlier screening invitation, this situation may be referred to as serial screening. When continuous screening is made available only to individuals who had tested previously, population member response is referred to as repeat screening. This study assessed adherence to serial- and repeat-colorectal cancer screening among older adult members of an independent practice association-type health maintenance organization (HMO) in two consecutive rounds of screening. In the first screening round, fecal occult blood tests (FOBTs) were sent to 1,565 subjects who were randomly assigned to receive usual care or behavioral interventions intended to encourage testing. Overall, 647 (41%) subjects completed and returned their tests. In the second screening round, FOBTs were mailed again to all subjects; however, the interventions were discontinued. Logistic regression analysis results shows that first-round testing was a significant independent predictor of serial adherence for subjects older than 65 years of age (odds ratio[OR] = 10.8) and those younger than 65 years of age (OR = 10.9); and a significant negative association between exposure to first-round intervention and serial adherence (OR = 0.5) was found among younger subjects. Among first-round adherers, age was significantly and positively related to repeat adherence (OR = 1.6). However, exposure to first-round intervention and having an abnormal FOBT result were significantly and negatively associated with repeat adherence (OR = 0.5 and OR = 0.4, respectively). The results of this study reported here indicate that previous screening is a strong predictor of serial adherence, and special efforts may be required to achieve high levels of serial and repeat adherence among younger adults. Additional research is needed to understand why persons with abnormal screening test results are unlikely to engage in repeat screening.