Changes in best friendship quality during adolescence coincide with the emergence of romantic relationships. This study aimed to examine the extent to which changes in friendship quality (intimacy, conflict, emotional support) between the ages of 16 and 22 varied according to four romantic involvement patterns (Late, Sporadic, Long-Term, Frequent) followed during this period. Gender was also included as a moderator. Participants (n = 281; 61% girls) identified their romantic partners and reported on the quality of their relationship with their best friend each year. A series of multilevel growth curve models revealed that participants in the Late involvement group reported an increase in conflict with their best friend during this period; those in the Sporadic involvement and Frequent involvement groups reported increases in intimacy; and youths in the Long-Term involvement group reported no changes in friendship intimacy, conflict, or emotional support over time. Thus, among youths who reported changes in best friendship quality between adolescence and emerging adulthood, the observed changes appeared to vary according to the romantic involvement patterns followed during this period.