OBJECTIVE: Conference searching is a common part of systematic review methodology, this study investigates what proportion of study/trial data included in systematic reviews of pharmacologic interventions is derived solely from data published in conference abstracts, for 3 different disease areas. METHODS: The Cochrane Library of systematic reviews (SRs) was searched for SRs on pharmacologic interventions which state that they include conference abstracts in their Specialized Registers and include conference searching as part of the stated SR methods. Included studies lists of completed systematic reviews were reviewed and the total number of included studies and the number of studies for which data was obtained only from conference abstracts were extracted. In disease areas where a large number of SRs met the inclusion criteria, the 10 most recently published SRs were selected. The following disease groups were considered: psychological disease (depression and bipolar disorder), female cancers (breast cancer and ovarian cancer), and arthritis (osteoarthritis and rheumatoid arthritis). RESULTS: 3/10, 9/10 and 4/10 SRs contained studies solely from conference abstracts, for psychological disease, female cancers and arthritis respectively. For psychological disease 5% (5/226) of all studies included in 10 SRs came only from conference abstracts, for female cancers this was 14% (31/220) and for arthritis this was  14% (33/232). CONCLUSIONS: The proportion of studies from conference abstracts only included in SRs varies in the 3 examined disease areas. From these results, there is some evidence to suggest that the disease area of the review should inform the decision of whether to include conference searching as part of the protocol. To answer this question more conclusively, a more expansive review of SRs should be conducted covering a greater number of SRs and disease areas.