Prior research, based on the analysis of aggregate-level state legislative election data, has documented a decline in the marginality of state legislative districts. Over the past twenty or so years, state legislators, much like congressional incumbents, have been winning reelection by larger margins of the vote. By taking advantage of district-level, state legislative election data, the research presented here specifies the relative impact of incumbency on district marginality, while controlling for statewide party trends. More specifically, it follows the lead of congressional elections studies, examining the impact of retirement slump and sophomore surge on the legislative district vote. In general, the legislative district vote reflects both a retirement slump and a sophomore surge, with the magnitude of their impact being conditioned by the level of contested incumbent victories in a state.Since the mid-sixties, congressional incumbents have sought and won reelection at higher rates, and their margins of victory have increased over time (Erikson ). At the congressional district level, a party's share of the vote increases over its previous share when its freshman incumbent runs for a second term (i.e., sophomore surge), and decreases below its previous share when its incumbent does not run for reelection (i.e., retirement slump;Erikson 1971;Mann 1978).During the last decade, we have learned much from survey data about the incumbency advantage in congressional elections. The increased visibility of congressional members in such areas asThe author would like to thank the three anonymous reviewers for their constructive criticism and Malcolm E. Jewell for his significant contribution to this research.