Research suggests that the timing and sequence of sexual identity development milestones impact myriad health and mental health outcomes for sexual minority youth. Because these milestone events are typically assessed retrospectively, traditional data collection approaches are limited by recall bias and lack of precision in the recording of milestone events, which may conceal the distinctions between events and distort the recording of youth's developmental trajectories. The purpose of this exploratory study was to compare responses to questions about psychosexual milestones elicited by a Life History Calendar and a self-administered survey. Results indicated discrepancies in the reported occurrence and timing of milestone events between the two data collection methods. Differences in the timing of specific milestone events ranged from two months to 15 years. Implications of these discordant findings for sexual minority youth are discussed. (Contains 6 figures, 1 table, and 2 notes.)