The authors examined the relationship between fibrin degradation products (FDP) and outcome in children with isolated head injury by reviewing the records of 69 children who met the following criteria: (1) less than 16 years of age; (2) diagnosis of isolated head injury and (3) FDP levels. Outcome was evaluated using the following Glasgow Outcome Scale (GOS): 1 = death; 2 = vegetative state; 3 = functionally impaired; 4 = minimal dysfunction; 5 = premorbid level of functioning. Poor outcome was defined as GOS 1-3. Twenty-nine of 33 patients with FDP > 1000 (g/mL had GOS scores < 4 compared to 4/36 patients (11%) with FDP < 1000 microg/mL (Fisher's Exact Probability Test P < .0001). When stratified by GCS, no other prognosticator of outcome was needed when GCS was < 7 and > 12. In patients with GCS 7-12, however, 4/6 with FDP >1000 microg/mL had a poor outcome and all 12 patients with FDP < 1000 microg/mL had a good outcome (P = .004). The authors conclude that FDP > 1000 microg/mL predicts poor outcome in children with isolated head injury. Fibrin degradation products are a strong independent prognosticator of outcome in children when GCS is between 7 and 12.