Online courses at the college level are growing in popularity, and nearly all community colleges offer online courses (Allen and Seaman in "Tracking online education in the United States," Babson Survey Research Group, Babson Park, 2015). What is the effect of the expanded availability of online curricula on persistence in the field and towards a degree? We use a model of self-selection to estimate the effect of taking an online course, using region and time variation in Internet service as a source of identifying variation. Our method, as opposed to standard experimental methods, allows us to consider the effect among students who actually choose to take such courses. For the average person, taking an online course has a negative effect on the probability of taking another course in the same field and on the probability of earning a degree. The negative effect on graduation for students who choose to take an online course is stronger than the negative effect for the average student. Community colleges must balance these results against the attractive features of online courses, and institutions may want to consider actively targeting online courses toward those most likely to do well in them.