Klinefelter syndrome is an underdiagnosed chromosomal disorder that has significant implications for health and for medical management. This report presents 5 adult male patients diagnosed with previously unsuspected Klinefelter syndrome as a result of cytogenetic testing for suspected hematologic malignancies. This case series highlights the importance of maintaining a comprehensive and holistic approach to medical care. The medical, genetic, and psychosocial implications of the Klinefelter diagnosis are discussed.