Background Older adults are commonly accompanied to routine medical visits. Whether and how family companion behaviours relate to visit processes is poorly understood. Objective To examine family companion behaviours in relation to older adults' medical visit processes. Design and participants Observational study of 78 accompanied primary care patients ages 65 and older. Main outcome measures Medical visit communication (coded using RIAS), patient verbal activity (as a proportion of visit statements) and visit duration (in min), from audio recordings. Results Companions' facilitation of patient involvement was associated with greater patient question asking (P = 0.017) and orienting statements, less passive agreement (P = 0.004) and social talk (P = 0.013) and visits that were 3.4 min longer (P = 0.025). Facilitation of patient understanding was associated with less physician question asking (P = 0.004), visits that were 3.0 min longer (P = 0.031), and lower patient verbal activity (30.3% vs. 36.9% of visit statements; P = 0.028). Facilitation of doctor understanding was associated with greater patient biomedical information giving (P = 0.049). Autonomy detracting behaviours were not associated with visit duration but were associated with lower levels of patient verbal activity (36.3% vs. 29.1% of visit statements; P = 0.041). When companions assumed more behaviours, medical visits were incrementally longer (16.1, 19.5, 21.7 min, corresponding to 0–1, 2–4 and 5+ behaviours; P < 0.001 both contrasts), and patients were less verbally active (35.6%, 33.9%, 27.1% of visit statements; P = 0.09 and P = 0.009, respectively). Discussion Behaviours assumed by patients' companions were associated with visit communication, patient verbal activity and visit duration. Conclusions Interventions to capitalize on family companions' presence may benefit medical visit processes.