Background Papers retracted for fraud (data fabrication or data falsification) may represent a deliberate effort to deceive, a motivation fundamentally different from papers retracted for error. It is hypothesised that fraudulent authors target journals with a high impact factor (IF), have other fraudulent publications, diffuse responsibility across many co-authors, delay retracting fraudulent papers and publish from countries with a weak research infrastructure. Methods All 788 English language research papers retracted from the PubMed database between 2000 and 2010 were evaluated. Data (...) pertinent to each retracted paper were abstracted from the paper and the reasons for retraction were derived from the retraction notice and dichotomised as fraud or error. Data for each retracted article were entered in an Excel spreadsheet for analysis. Results Journal IF was higher for fraudulent papers (p<0.001). Roughly 53% of fraudulent papers were written by a first author who had written other retracted papers (‘repeat offender’), whereas only 18% of erroneous papers were written by a repeat offender (χ=88.40; p<0.0001). Fraudulent papers had more authors (p<0.001) and were retracted more slowly than erroneous papers (p<0.005). Surprisingly, there was significantly more fraud than error among retracted papers from the USA (χ2=8.71; p<0.05) compared with the rest of the world. Conclusions This study reports evidence consistent with the ‘deliberate fraud’ hypothesis. The results suggest that papers retracted because of data fabrication or falsification represent a calculated effort to deceive. It is inferred that such behaviour is neither naïve, feckless nor inadvertent. (shrink)