Background: Cholesterol and cholesterol metabolism, involved in continued neural plasticity, has been associated to suicide and suicidal behavior. Apolipoprotein E (ApoE) plays an important role in the cholesterol metabolism. The purpose of this study was to investigate whether ApoE in cerebrospinal fluid was related to severity of suicidal behavior as measured by number of earlier suicide attempts, reversibility/interruptabilty and violent method of suicide attempt. Methods: CSF ApoE and 5-hydroxyindolacetic acid (5-HIAA) were measured in 42 medication free suicide attempters. Earlier suicide attempts and the reversibility of suicide attempt method were assessed with the Suicide Intent Scale (SIS) and the Freeman Scale. Suicide attempts were classified according to violence of method. Results: CSF ApoE levels significantly negatively correlated to the scores on Freeman Reversibility and there was a trend for lower CSF ApoE levels in suicide attempters using a violent method. Patients with at least one earlier suicide attempt (repeaters) showed a trend for higher CSF ApoE levels compared to suicide attempters debuting with suicidal behavior at inclusion in the study. The correlation between CSF ApoE and 5-HIAA was not significant. Limitations: The main limitations to this study were a relatively small sample size and lack of a healthy control group. Conclusion: Irreversible suicide attempts, representing a high risk for completed suicide, may be associated with lower level of ApoE in CSF.