Underreporting of medication errors poses a threat to quality improvement initiatives. Hospital risk management programs encourage medication error reporting for effective management of systems failures. This study involved a survey of 156 medical-surgical hospitals in the United States to evaluate systems factors associated with the reporting of serious medication errors. Prior to controlling for bed size, a multivariate logistic regression model showed increased reporting of medication errors in hospitals with 24-h pharmacy services, presumably because of better error reporting systems. When number of occupied beds was included, the final model demonstrated bed size to be the only statistically significant factor. Increased reporting rates for serious medication errors warrant further evaluation, but higher error reporting may paradoxically indicate improved error surveillance. Results suggest that increased availability of pharmacist services results in opportunities for more diligent systematic efforts in detecting and reporting medication errors, which should lead to improved patient safety.