Low muscle strength, functional score at discharge, and complications during a ten-day rehabilitation hospital stay can affect mortality rates in bedridden geriatric patients. This was a prospective observational study in a cohort of 105 bedridden geriatric patients admitted to the Rehabilitation ward after a major illness or surgery. All participants had a severe dependency on another person (Barthel’s Index < 60). The one-year mortality rate in this cohort was 15.2%, with further subdivision according to the number of complications: 61.5% in patients with ≥3 complications during hospitalization, 17.6% in patients with two complications, 9.5% with one complication, and 3% in patients with no complications. The Barthel Index at discharge (OR = 0.95; p = 0.003) and ≥3 medical complications (OR = 8.33; p = 0.005) during rehabilitation ward stay were significant predictors for one-year mortality. The odds of one-year mortality after discharge increased eightfold in patients with ≥3 medical complications. Sarcopenia, age, and sex were not significant predictors of mortality in this cohort. The 10-day acute rehabilitation was too short to achieve progress from severe to moderate independence in 60% of patients. The Barthel Index at discharge and a number of complications affect the mortality rate. These findings provide valuable insights into the complex dynamics of mortality and functional outcomes in bedridden geriatric patients.