We examined the sensitivity and the accuracy of three health databases (hospital discharge data, death certificates and pathologic records) between 1997 and 2001 in an Italian community, to evaluate their accuracy for the diagnosis of lymphoid malignancies and their ability to detect newly diagnosed patients affected by these diseases. Hospital discharge data showed the best sensitivity among the examined databases, though they exhibited an unexpectedly high number of diagnostic errors, even when limiting the analysis to patients with repeated hospital admissions over time. Overall, the pathologic registry and the death certificate file showed a higher diagnostic accuracy, though their sensitivity was considerably lower than hospital discharge data.