The present study provides experimental data comparing emerging adults’ attitudes toward dating and sibling violence in adolescence using a new methodology in which participants observe a violent interaction between adolescents. The reported amount of violence experienced in dating and sibling relationships among emerging adults is also compared. The participants included 148 emerging adults (111 females, 37 males) who were in the dating violence condition and 134 emerging adults (93 females, 41 males) in the sibling violence condition. The results provide initial psychometric data on a new measure to assess attitudes toward interpersonal violence in adolescence—the Attitudes toward Interpersonal Violence Assessment ( AIVA). Using this new observational measure in an experimental design, empirical evidence was found that (1) male initiated violence was less acceptable than female initiated violence, (2) females were less accepting of violence than males, (3) individuals were more complacent toward sibling violence than dating violence in adolescence, (4) males reported perpetrating more injuries than females, and (5) sibling violence was reported at higher frequencies than dating violence. Implications of the findings are discussed.