Prebasic molt of the primaries in most species of northern hemisphere gulls occurs between April and December (Dwight 1925, Grant 1986, Cramp and Simmons 1983, pers. obs.). Exceptions are mainly transequatorial migrants, both those that molt primaries after they have reached their southern hemisphere winter grounds (e.g., Sabine's Gull, Xema sabini; Grant 1986), and those that suspend primary molt between the summer and winter grounds (e.g., Baltic Lesser Black-backed Gull, Larus fuscus fuscus; Jonsson 1998). The complete second prebasic molt of the Black-legged Kittiwake (Rissa tridactyla) reportedly occurs from May to November, the adult prebasic molt from June to December (Cramp and Simmons 1983, Baird 1994). During the spring of 1999, we noted adult Black-legged Kittiwakes in central California that had not completed their prebasic primary molt. Here we document and discuss this phenomenon.