In a series of 93 emergency patients, 58 were classified as concussions on a clinical basis. Thirteen of the patients with concussion had increased levels of creatine kinase isoenzyme BB (CK-BB) in their cerebrospinal fluid (CSF). We performed a prospective, follow-up investigation comparing 10 patients with a CK-BB increase and 10 patients without a CK-BB increase after concussion. Within 24 hours, at 6 months and 3 years after concussion, each patient was subject to a special interview to obtain pre-concussional baseline data and post-concussional follow-up data concerning their complaints and capacity for daily activities. We found a definite change towards increasing disability in 8 of the 10 patients with a raised CK-BB, and in only 1 of the 10 patients with normal levels of CK-BB. A careful neuropsychological examination confirmed inferior performance in tests especially sensitive to brain injury in patients with a CK-BB increase. Our results suggest that increased levels of CK-BB after concussion signify a more severe injury which is not found in the clinical examination during the first days after the accident, and that these patients are a high-risk group for the development of post-concussional problems and symptoms.