Background A high proportion of the information about the patients' medication from the electronic health record contains some error. The importance of these errors has not been studied.

Purpose To analyse the importance of the errors contained in the Electronic Health Record EHR relating to patients' usual medication.

Materials and methods The information about medication contained in the EHR-D was analysed including all patients with surgical admission between February and November 2010. The errors taken into account were: medicine omitted (error by default), medicine added (error by excess) or medicine with incorrect dose/regimen. Important errors were considered the ones that affected to target medicines, that were: A) medicines with specific management in surgical patients, and B) medicines that have to be reconciled in the first 24 h of the admission in hospital. The proportion of patients with some errors was determined and the average number of errors, for both, general and important errors.

Results 167 patients were included, whose EHR-D were found registered an average of 7.8 (CI 95% 7.1 to 8.5) medicines. The 79.6% (N=133) of the EHR-D contained some errors, being found an average of 4.2 (CI 95% 3.6 to 4.7) errors/patient. The distribution by type of error was: 2.8 (CI 95% 2.3 to 3.3) errors by excess, 0.4 (CI 95% 0.3 to 0.6) errors by default and 1, 0 (CI 95% 0.8 to 1.2) errors of incorrect dose/regimen medication. The importance of errors affected to the 62, 9% (N=105) of the histories, with an average of 2.3 (CI 95% 2.0 to 2.5) errors/patient, being 1.2 (CI 95% 1.0 to 1.5) by excess, 0.3 (CI 95% 0.2 to 0.4) by default and 1, 2 (CI 95% 1.0 to 1.5) by incorrect dose/regimen medication.

Conclusions Eight out of ten EHR-D contain some error in their registrations of medication, and in six out of ten these errors are considered to be important. Half of the errors found are important ones. The information of the EHR-D should be verified before being used to carry out the reconciliation at the moment of the admission in hospital.