Background:
Identifying existing guidelines relevant to a topic is necessary for guideline panels to avoid duplication. Most guideline development handbooks provide strategies for retrieving similar guidelines.

Objectives:
To compare the strategies for retrieving existing guidelines in international guideline development handbooks.

Methods:
We systematically searched the PubMed and TRIP databases using terms 'handbook', 'toolkits' or 'manual'; we searched Google and the websites of guideline development organizations and checked the references of the handbooks identified as a supplementary search. We extracted information about the organization, update year, search resources and search terms.

Results:
We identified 16 guideline development handbooks from agencies including the World Health Organization (WHO), the National Institute for Health and Care Excellence (NICE), the Scottish Intercollegiate Guidelines Network (SIGN) and the Agency for Healthcare Research and Quality (AHRQ), which were published from 1998 to 2012. Among these, 12 handbooks (75%) reported the need to retrieve existing relevant guidelines before guideline development, three (19%) did not report searching methods, seven (44%) only reported the search resources and only two (13%) provided a detailed strategy for searching for existing guidelines. Furthermore, various search terms were presented in the handbooks; the most common terms were 'guideline' and 'recommend*'. The most common resources were National Guideline Clearinghouse (NGC) (eight, 50%), NICE (six, 38%), SIGN (five, 31%) and MEDLINE (four, 25%).

Conclusions:
Few handbooks reported a detailed search strategy and the terms used varied. A standardized search strategy for existing guidelines is required.

Patient or healthcare consumer involvement:
None.