This paper examines post-adoption behavior (continued adoption versus discontinuance) within the context of online service use. Innovation diffusion theory is used as a theoretical framework to extend information technology adoption research to the case of post-adoption behavior. This theory is used to formulate 11 research hypotheses distinguishing discontinuers from continuing adopters and exploring reasons behind their discontinuance (replacement versus disenchantment). These hypotheses were then empirically tested using data collected from a field survey of online service users. Our results indicate that potential discontinuers can be discriminated from continued adopters based on their sources of influence (external and interpersonal), perceived service attributes (usefulness and compatibility), service utilization, and network externality (complementary product usage), during their time of initial adoption. We also found that later adopters are more likely to discontinue due to disenchantment than replacement, and are more influenced by interpersonal sources and utilize the service less during their adoption period than replacement discontinuers. Implications for research and practice are drawn.