Usual care after hip or knee joint replacement does not adequately address the problem of low physical activity levels. We aimed to determine whether exercise delivered in a group setting in the early stage of outpatient rehabilitation influenced self-reported physical activity levels after hip or knee joint replacement. A case series of 79 participants referred to a 6-week outpatient orthopaedic exercise group after total hip or knee replacement were evaluated using the International Physical Activity Questionnaire (IPAQ) short form. Physical function was evaluated using Osteoarthritis Research Society International (OARSI) recommended performance-based tests (30 s Chair Stand Test, 40 m Fast Pace Walk Test, Stair Climb Test, Timed Up and Go Test, 6 Minute Walk Test). Measures were assessed at admission, discharge and 6 weeks after group discharge. Non-parametric analysis was conducted for IPAQ scores. Analysis of functional measures was conducted with linear mixed models with time modelled as a repeated measure. Standard multiple regression and correlation analysis were conducted. Fifty-four participants completed the study. Self-reported activity levels improved significantly at program discharge but not at 6-week follow-up. All performance-based measures improved significantly at program discharge. Fast-paced walking and 6 Minute Walk Test measures continued to improve at 6-week follow-up. Group dynamics present in an outpatient rehabilitation exercise program may increase physical activity levels during group participation but not after group cessation. Performance in all functional measures improved at group discharge.