Patient safety is a major concern in today's healthcare, therefore, development of a competent workforce is of utmost importance. Literature reflects insufficient number of studies related to telemetry monitoring competency of nurses. This study determined the reliability and validity of a telemetry monitoring competency tool developed by the author using psychometric theory principles of measurement. The data analysis showed the tool has good content validity with CVI scores of 0.89 and 0.99 using Lawshe's (1975) and Lynn's (1986) methods, respectively. For inter-rater reliability, the tool demonstrated moderate strength of agreement (¿ = 0.58) in the written method of evaluation and substantial strength of agreement (¿ = 0.78)in the clinical observation method of evaluation. The major limitation for the inter-rater reliability testing was the small sample size. Application of appropriate theoretical framework and evidence-based practices contributed to the favorable results obtained in this study. Implementation of the Telemetry Monitoring Competency Tool© for use in determining competency of nurses in the practice setting is very promising .