Background: Cochrane systematic reviews provide more convincing and reliable evidence needed for clinical decision making, based on rigorous processes. From protocol to review is one of the important links. Objectives: To describe the proportion of protocols in the Cochrane Database of Systematic Reviews (CDSR); and to provide insight into the process of conversion. Methods: We searched Issue 1, 2009 of CDSR to acquire data on published protocols and reviews. The proportions of protocols were analyzed by factors of publishing years and Cochrane groups. Results: There were 5676 articles published in Issue 1, 2009 of CDSR, of which 1939 (34%) were protocols. The 27 most prolific review groups (more than 100 reviews/protocols published) are listed in Figure 1. The average number of protocols in each of the 51 groups was approximately 37% (range 14% to 65%; half > 40%). More than 800 (41%) protocols were published at least three years ago (from 1996 to 2006). From 2001 to 2006, the ratio of new protocols to new reviews was 43/212, 79/218, 109/300, 131/348, 152/405, 213/582. One-hundred-sixty-two protocols have been withdrawn. Conclusions: There are four steps to complete a Cochrane systematic review: title, protocol, review and update. The whole course needs about two years. There are a significant number of protocols in CDSR that have been published for more than three years. Attention is needed to improve the efficient conversion of protocols to reviews.