Readers of scientific articles often read only the abstract and its conclusions because of lack of time or of access to the full-length articles.

To assess the prevalence of misleading conclusions in abstracts of randomized controlled trials (RCTs) in rheumatology, determine whether trials are registered and whether abstract conclusions are based on the primary outcome (PO), and identify the predictors of misleading abstract conclusions.

We searched Medline, Embase and the Cochrane Collaboration for reports of RCTs assessing rheumatoid arthritis, osteoarthritis or spondylarthropathies published between January 2006 and April 2008. Abstract conclusions were misleading if: the PO was not reported in the conclusion; the conclusions were based on only a secondary outcome or subgroup results; the results and conclusions were in disagreement; negative results were suggested as equivalent, or if there was no discussion of benefits and risks in cases of serious adverse events.

Of the 144 reports selected, we focused on the 105 articles containing a clear PO. Twenty-four reports (23%) contained misleading conclusions. Lack of PO reporting (n=10) and conclusions disagreeing with article results (n=7) were the most frequent reasons. Nineteen out of 144 (13.2%) declared study registration with clear and similar registered and published POs and no misleading abstract conclusions. Reports of negative results showed a higher frequency of misleading conclusions as did those assessing osteoarthritis. On multivariable analysis, only negative results predicted misleading abstract conclusions (OR=9.58 [3.20–28.70]).

Almost one-quarter of these RCT in rheumatology had misleading conclusions in the abstract, especially those with negative results.