Purpose: Preparing bone marrow smears using non-anticoagulated bone marrow aspirate is a traditional practice but many laboratories now use anticoagulated aspirate samples in K-EDTA. There are no published studies comparing the effectiveness of these two methods. This report compares the readability of slides, prepared using non-anticoagulated and anticoagulated methods, from three laboratories in Hamilton Ontario. Methods: A blinded set of 129 aspirate slides prepared using anticoagulated and non-anticoagulated methodologies (using K-EDTA) was reviewed by three reviewers. Slides were classified as unreadable if two of the three observers rejected them based on a standardized survey. Results: The proportion of slides classed as unreadable varied widely (5.0% to 46.9%) depending on collection and slide preparation methods. Degree of coagulation did not affect readability. Conclusion: A measurable advantage to using non-anticoagulated bone marrow was not demonstrated. Immediate anticoagulation of bone marrow samples, with laboratory personnel at the bedside to assess sample quality, followed by slide preparation in the laboratory provided the best results.