Klinefelter's Syndrome is a sex chromosome abnormality that exhibits more than one X allele in affected males. Klinefelter's males are typically tall and have a high occurrence of testicular atrophy; otherwise they are normal in appearance. Although most forensic laboratories do not have the capability of karyotyping samples to determine the presence of this anomaly, current STR methods do give the forensic DNA analyst the ability to observe possible genetic defects in a sample. In the current study, whole blood was obtained from two suspected Klinefelter males (adjudicated case samples) and five diagnosed Klinefelter males. DNA was extracted from all seven samples by organically using the phenol chloroform method, followed by concentration in Centricon 100 tubes. The DNA was then quantitated by using the quantiblot Human DNA Quantitation Kit. For corroboration of a possible genetic abnormality (i.e., Klinefelter's Syndrome), additional testing of the sample extracts was conducted by using X-Y specific STR's. Amplification and typing of three X and two Y chromosomal STR's was accomplished. This same line of testing should also be useful for other sex chromosome disorders as well as other genetic aberrations caused by chromosome nondisjunction. 1 table, 2 figures, and 10 references