Abstract The objectives were to determine the phenotypic correlations between biometric characteristics and obtain predictive functions of vicuna body weight (BW) at shearing. Measurements were recorded in 69 males and 119 females in the area of influence of the Campesino Community of Huachocolpa, Huancavelica region of Peru, during the annual management for the shearing or "chaccu", in 2017. The animals were also classified by age into adults (90) and juveniles (98). The measurements taken were: BW at shearing, head length, neck length, wither height, back height, rump height, girth (thoracic perimeter), body length, metatarsal perimeter, rump length, abdominal length and back length. Data were analysed by regression modelling following log10 transformation. Body volume was estimated using girth and body length measurements. BW varied between 20–52 kg. While male vicunas were heavier and longer than females and adult vicunas were heavier, higher, longer and had a greater girth compared with juvenile vicunas the best predictive model for BW included terms only for body volume and wither height. Sex and age were not significant. Using log10 girth measurements and sex accounted for 55% of the variance in BW. Using girth measurements and body length, to estimate body volume, and wither height accounted for 64% of the variance in BW.