Immobilization of critically ill patients leads to muscle weakness, which translates to increased costs of care and long-term functional disability. We tested the validity of a German Surgical Intensive Care Unit (ICU) Optimal Mobilization Score (SOMS) in 2 different cohorts (neurocritical and nonneurocritical care patients).Physical therapists estimated the patients' mobilization capacity by using the German version of the SOMS the morning after admission. We tested the prognostic value of the prediction for ICU and hospital length of stay (LOS) as well as for mortality, and built a model to account for other known predictors of these outcomes in the 2 cohorts.A total of 128 patients were included in the analysis, 48 of these were neurocritical care patients. The SOMS predicted mortality and ICU and hospital LOS. Neurocritical care patients stayed significantly longer in the ICU (median 12 vs 4 days, P < .001) and in the hospital (25 vs 17 days, P = .02). The SOMS predicted ICU and hospital LOS. It predicted mortality only in nonneurocritical patients.The German SOMS assessed by physical therapists on the day after ICU admission predicts ICU and hospital LOS, and mortality. Our data suggest that the association between early mobilization and mortality is more complex in neurocritical care patients.