Whether based on self-reported disability or direct physical measurements, studies of upper body function (UBF) among women with breast cancer consistently reveal high prevalence of limitation. Unfortunately, limited research and conflicting results undermine the ability to identify those factors that contribute to these UBF problems. This study describes the influence of selected personal and treatment characteristics on UBF, six-months following treatment for unilateral breast cancer, in a population-based sample of women residing in Southeast Queensland, Australia (n = 214). UBF was assessed by three objective measures (upper body strength and endurance, flexibility and hand grip strength) and two subjective measures (Disability of the Arm, Shoulder and Hand questionnaire and arm morbidity scale of the Functional Assessment of Cancer Treatment, Breast questionnaire). Modest correlations between the various UBF measures suggest that each captures a somewhat different dimension of physical function and disability. Advancing age, being treated on the non-dominant side, more childcare responsibilities, lower socioeconomic status, more extensive lymph node removal, having lymphoedema, and UBF scores of the untreated side emerged as significant correlates depending on whether UBF was assessed objectively or subjectively. There also was evidence that the relationships between the UBF measure of flexibility and (i) radiation treatment and (ii) side of treatment were modified depending on dominance. These results highlight the necessity of taking dominance into account when assessing functional impairment among breast cancer survivors. The findings also highlight the importance of considering whether subjective or objective UBF measures are more relevant in the design of future studies.