The evidence supports the benefits and safety of physical activity in all stages of the cancer care pathway. In the pretreatment phase, regressing physical activity levels exposes cancer patients to several risks. This study aims to identify factors associated with the patient's physical activity levels before treatment. This is a cross-sectional study conducted by questionnaire. Participants were patients hospitalized before the start of treatment. Sociodemographic characteristics were assessed. Physical activity level was measured by the International Physical Activity Questionnaire, functional independence by the Barthel Index, anxiety and depressive symptomatology by the Hospital Anxiety and Depression Questionnaire, and pain by the numerical rating scale. Statistical analysis was performed to look for statistical associations between physical activity level and the other variables (Mann-Withney U test). The results showed that the level of activity in 63.49% of the participants was low; otherwise, it was moderate. The low level of physical activity seems to be associated with advancing age (p=0.035), increasing pain (p=0.002), and declining functional independence (p=0.000). Engagement in moderate physical activity appears to be associated with decreased depressive and anxiety symptomatology (p=0.000) and physical activity advice given by health professionals alone or with family and friends (p=0.034). The results found in participants before the initiation of cancer treatment call for intervention within a comprehensive, family-centered approach. Intervention through physical activity education should be adopted shortly after a cancer diagnosis.