Recent evidence suggests that young sexual minority men's sexual position identities (e.g., "top," "bottom," "versatile") may be governed by dynamic influences. Yet, no study has prospectively examined whether, how, and why this aspect of sexual minority men's sexuality changes over time. Consequently, the present study investigated the extent to which young sexual minority men use sexual position identities consistently over time, typical patterns of position identity change, explanations given for this change, and the correspondence of changing sexual position identities with changing sexual behavior and fantasies. A total of 93 young sexual minority men indicated their sexual position identity, behavior, and fantasies at two assessment points separated by 2 years. Following the second assessment, a subset (n = 28) of participants who represented the various sexual position identity change patterns provided explanations for their change. More than half (n = 48) of participants changed their sexual position identity. Participants showed a significant move away from not using sexual position identities toward using them and a significant move toward using "mostly top." Changes in position identity were reflected, although imperfectly, in changes in sexual behavior and largely not reflected in fantasy changes. Participants offered 11 classes of explanations for their identity changes referencing personal development, practical reasons, changing relationships, and sociocultural influences. Previous investigations of sexual minority men's sexual position identities have not adequately attended to the possibility of the changing use of the sexual position categories "top," "bottom," and "versatile" across young adulthood. Results of the present study suggest the possibility of a more fluid, context-dependent use of these terms than previously documented.