Immobilization and subsequent weakness are consequences of critical illness. Despite the theoretical advantages of physical therapy to address this problem, it has not been shown that physical therapy initiated in the intensive care unit offers benefit. Prospective cohort study in a university medical intensive care unit that assessed whether a mobility protocol increased the proportion of intensive care unit patients receiving physical therapy vs. usual care. Medical intensive care unit patients with acute respiratory failure requiring mechanical ventilation on admission: Protocol, n = 165; Usual Care, n = 165. An intensive care unit Mobility Team (critical care nurse, nursing assistant, physical therapist) initiated the protocol within 48 hrs of mechanical ventilation. The primary outcome was the proportion of patients receiving physical therapy in patients surviving to hospital discharge. Baseline characteristics were similar between groups. Outcome data are reflective of survivors. More Protocol patients received at least one physical therapy session than did Usual Care (80% vs. 47%, p < or = .001). Protocol patients were out of bed earlier (5 vs. 11 days, p < or = .001), had therapy initiated more frequently in the intensive care unit (91% vs. 13%, p < or = .001), and had similar low complication rates compared with Usual Care. For Protocol patients, intensive care unit length of stay was 5.5 vs. 6.9 days for Usual Care (p = .025); hospital length of stay for Protocol patients was 11.2 vs. 14.5 days for Usual Care (p = .006) (intensive care unit/hospital length of stay adjusted for body mass index, Acute Physiology and Chronic Health Evaluation II, vasopressor). There were no untoward events during an intensive care unit Mobility session and no cost difference (survivors + nonsurvivors) between the two arms, including Mobility Team costs. A Mobility Team using a mobility protocol initiated earlier physical therapy that was feasible, safe, did not increase costs, and was associated with decreased intensive care unit and hospital length of stay in survivors who received physical therapy during intensive care unit treatment compared with patients who received usual care.