Ultrasonic measurements of the longitudinal absorption and velocity and shear impedance were made over a large range of temperatures in the weakly associated liquid isobutyl bromide. Evidence was found for the coexistence of four different relaxation mechanisms. Above −50°C rotational isomeric relaxation exhibiting a single relaxation time was found. Vibrational relaxation also appears to be present with a relaxation time shorter than that usually found in nonassociated liquids. The dispersion and absorption data below −125°C showed that both shear and structural relaxation effects were present. The former was related to a distribution of relaxation times. The coexistence of these several relaxations is consistent with the concept that a weakly associated liquid should show relaxation behavior typical of both strongly and nonassociated liquids.