Background: Cognitive symptoms, such as concentration problems, are frequently recorded by sarcoidosis patients. Objectives: The aim of this study was to assess the prevalence of perceived everyday cognitive failure in sarcoidosis patients and healthy controls. Furthermore, the effect of treatment on cognitive functioning was examined. Methods: The study included 343 sarcoidosis patients (44.6% females; age 49.3 +/- 11.0 years). They completed the Cognitive Failure Questionnaire (CFQ) and Fatigue Assessment Scale (FAS) at baseline and the 6-month follow-up to evaluate the effect of treatment on cognitive functioning. The control group consisted of 343 age- and sex-matched healthy controls. Results: The mean CFQ score was significantly higher in sarcoidosis patients (37.3 +/- 16.1) compared with the controls (31.3 +/- 10.1; p < 0.0001).A high CFQ sore (>/=43) was found in 35.0% of the patients and only 14.3% of the controls. No relation with disease severity and duration, or tumor location was found. The proportion of patients receiving treatment did not differ among the groups with high and normal CFQ score. At the 6-month follow-up, only patients recently treated with anti-TNF-alpha therapy (n = 42) demonstrated a significant improvement in the CFQ score (Delta -7.07 +/- 7.23) compared with the untreated patients (Delta -0.08 +/- 9.35) and patients treated with prednisone with or without methotrexate (Delta 1.67 +/- 9.22; p < 0.0001). After adjustment for the concomitant decrease in fatigue, the effect of anti-TNF-alpha therapy remained high and significant. Conclusions: Subjective cognitive failure is a substantial problem in sarcoidosis patients regardless of disease severity. Anti-TNF-alpha therapy had a positive effect on cognition, fatigue and other symptoms of sarcoidosis.