Trisomy 14 mosaicism is a rare cytogenetic abnormality with a defined and recognizable clinical phenotype. We present a detailed clinical history and physical findings of five patients with low-level mosaicism of trisomy 14 detected by array-based comparative genomic hybridization (array-CGH) analysis or by routine chromosome analysis. These patients exhibited growth and developmental delays with variable severity, congenital anomalies, pigmentary skin lesions, and dysmorphic features. The phenotype of our patients was compared with previously described cases. This report suggests that trisomy 14 mosaicism may be more common than has been previously appreciated and also illustrates the important application of array-CGH to detect low-level mosaic chromosome abnormalities. We predict that a wider application of the array-CGH technology will significantly increase the detection rate of low-level mosaicism and will subsequently improve our ability to provide a diagnosis for patients with dysmorphic features, congenital anomalies, and developmental delay.