When choosing among several options, people often defer choice. Previous research found that choice deferral can increase and/or decrease as the number of available options increases. To understand these contradictory findings, the assumption was made that people may defer choice for either of two reasons. The number of deferrals made in a controlled laboratory experiment that were inferred to be due to no options being good enough, decreased as the number of options increased. In contrast, the number of deferrals inferred to be due to there being uncertainty regarding which option was the best, increased. Observing these two effects simultaneously helps to explain the inconsistent results observed in previous research. It is also shown that these assumptions can account for the various relationships previously observed between the size of the choice set and the probability of choice deferral. © 2009 Wiley Periodicals, Inc.