Social network analysis offers a high-resolution framework for understanding social influences on alcohol use, but full-length assessments confer significant burden, giving rise to brief measures. However, few studies have empirically compared brief and full-length assessments. To address this, the present study examined the internal and external validity of both brief and full egocentric social network assessments and their ability to capture weak social ties. In 405 adults (57.5% female) with alcohol use disorder, a full egocentric social network assessment estimated drinking behavior in the ego's 20 important alters, as well as their perceived closeness and frequency of interaction with their network, and the presence of supportive ties (mutual help organization members or treatment providers). The assessment yielded four social network drinking characteristics: percent drinking endorsement, percent heavy drinking endorsement, drinking frequency, and heavy drinking frequency. Measures from the full 20-alter assessment were compared to measures from the first 5 alters. Associations between brief and full network measures were of large magnitude ( = .53-.73, < .0001). Internal psychometric properties of the social network drinking characteristics were robust and similar in both assessments and, in terms of external validity, 13/16 (81.3%) associations of network drinking with the ego's drinking severity were equivalent across both assessments. However, the brief assessment had less representation of mutual help organization members and treatment providers ( < .01), resulting in a higher percent of alters endorsing drinking ( < .05). No other significant differences were present among other network drinking characteristics. These findings provide support for brief egocentric social network assessments, but also reveal limitations in characterizing potentially important weak social ties, namely the presence of mutual help organization members and treatment providers. Brief or full-length versions may be variably appropriate depending on the research and clinical aims. (PsycInfo Database Record (c) 2025 APA, all rights reserved).