Arachnoid cysts are frequent incidental findings on brain scans. Traditionally, they are regarded as harmless, congenital structures which do not require surgical treatment. In the rare cases where surgery is indicated it can be due to haemorrhage, hydrocephalus or cranial nerve affection caused by the cyst. However, recent literature suggests a correlation between arachnoid cysts and cognitive and affective symptoms. The hypothesised pathomechanisms include pressure, affected neuronal or glial metabolism and inflammation. If this is correct a more active approach might benefit the patients as suggested in this review.