Purpose: Neuromuscular abnormalities are common in ICU patients. We aimed to assess the incidence of clinically diagnosed ICU-acquired paresis (ICUAP) and its impact on outcome. Methods: Forty-two patients with systemic inflammatory response syndrome on mechanical ventilation for C48 h were prospectively studied. Diagnosis of ICUAP was defined as symmetric limb muscle weakness in at least two muscle groups at ICU discharge without other explanation. The threshold Medical Research Council (MRC) Score was set at 35 (of 50) points. Activities in daily living were scored using the Barthel Index 28 and 180 days after ICU discharge. Results: Three patients died before sedation was stopped. I-CUAP was diagnosed in 13 of the 39 patients (33%). Multivariate regression analysis yielded five ICU-AP-predicting variables (P \ 0.05): SAPS II at ICU admission, treatment with steroids, muscle relaxants or norepinephrine, and days with sepsis. Patients with ICUAP had lower admission SAPS II scores [37 ± 13 vs. 49 ± 15 (P = 0.018)], lower Barthel Index at 28 days and lower survival at 180 days after ICU discharge (38 vs. 77%, P = 0.033) than patients without ICUAP. Daily TISS-28 scores were similar but cumulative TISS-28 scores were higher in patients with ICUAP (664 ± 275) than in patients without ICUAP (417 ± 236; P = 0.008). The only independent risk factor for death before day 180 was the presence of ICUAP. Conclusions: A clinical diagnosis of ICUAP was frequently established in this patient group. Despite lower SAPS II scores, these patients needed more resources and had high mortality and prolonged recovery periods after ICU discharge.