Spreadsheets are commonly used to inform decision making across many business sectors, despite the fact that research performed in the financial sector has shown that they are quite error-prone. However, few studies have investigated spreadsheet errors and their impact in other domains, like the healthcare sector. This article derives a lifecycle-stage classification scheme of spreadsheet error types based on an aggregation of, and extension of, existing classifications. Based on these classifications, a case study is then presented, performed to investigate the prevalence of these spreadsheet error types in an Irish healthcare setting. Results reveal that more than 90% of the spreadsheets studied contained ` bottom-line' errors and the average cell-error rate was 13%. There was also a correlation between increased perceived impact of the spreadsheets and the number of errors identified. Recommendations from this research include providing spreadsheet training and guidelines for developers and users, and systematically managing and auditing spreadsheet development and use.