We present the clinical and molecular findings in a Turkish child with a de novo mosaic ring derived from chromosome 4 with multiple cell-lines; the karyotype was 46,XY,r(4)/45,XY, -4/47,XY,r(4),+r(4)/48,XY,r(4),+r(4),+dic r(4)/46,XY. The patient is a 20-month-old male who was the first pregnancy of nonconsanguineous parents. The baby was delivered at term with a birth weight of 1,700g (<3rd centile) and a length of 46 cm. The baby had feeding difficulties and vomiting problems. He started walking at age 2 years and delayed language was observed. Facial appearance was normal, but the ears were large with abnormal structure. The hands showed bilateral clinodactyly of the 5th fingers. He had mild mental retardation, and epilepsy. Analysis of chromosomes showed 46,XY,r(4)(::p16.3 -> qter::)/46,XY,r(4;4)(::p16.3 -> qter::p16.3 -> qter::) /46,XY by multicolor banding (MCB) technique. Array CGH delineated the size of the terminal deletion as 900 kb in 4p16.3. The Wolf-Hirschhorn critical region was preserved even though our patient had mild mental and motor retardation. While the mosaicism of the ring 4 could affect the phenotype, the deleted 900 kb distal deletion and clinical features of the patient may provide further insight into characteristic phenotype of the 4p- related syndromes. (C) 2009 Wiley-Liss, Inc.