Dysphagia has been strongly associated with poor hydration in acute stroke settings. However, in sub-acute settings, the contribution to dehydration of dysphagia in combination with other common stroke comorbidities has not been explored. The aim of this study was to investigate which demographic and stroke comorbidities, including dysphagia, contribute most significantly to oral fluid intake, hydration status and specific adverse health outcomes for patients in sub-acute rehabilitation following stroke. Data from 100 inpatients from three Australian rehabilitation facilities (14 with confirmed dysphagia and 86 without dysphagia) were analysed. Hierarchical multiple regressions were conducted to determine which demographic or stroke comorbidities were most predictive of each outcome: average daily fluid intake; Blood urea nitrogen/creatinine (BUN/Cr) ratio as an index of hydration and medically diagnosed adverse events of pneumonia, dehydration, urinary tract infection or constipation. Average daily beverage intake (M = 1448 ml, SD 369 ml) was significantly and independently predicted by Functional Independence Measure (FIM) at admission (F change = 9.212, p = 0.004). BUN/Cr ratio (M = 20, SD 5.16) was predicted only by age (F change = 4.026, p = 0.049). Adverse health events, diagnosed for 20% of participants, were significantly predicted by Admission FIM (OR 1.040, 95% CI 1.001, 1.081, p = 0.047). Dysphagia was not a significant predictor of any of the outcomes measured. Rather, overall functional dependency was the most significant predictor of poor oral fluid intake and fluid-related adverse health outcomes in sub-acute stroke. Clinical Trial number: Data for the post hoc analysis presented in this article came from the registered trial ACTRN12610000752066.