Abstract: Yang Fang, Hu Jintao, Zheng Lixiong, Yao Yongfeng, Song Biao, Sun Zhaojun, Shi Cuiping, Fang Sining Department of Dermatology and Venereology, Shenzhen People′s Hospital, The Second Clinical Medical College of Jinan University, Shenzhen 518020, China （Yang F, Zheng LX, Yao YF, Song B, Sun ZJ, Shi CP, Fang SN）; Department of Pathology, Shenzhen People′s Hospital, The Second Clinical Medical College of Jinan University, Shenzhen 518020, China （Hu JT） Corresponding author: Fang Sining, Email: 452290276@qq.com 【Abstract】 Objective To report a case of Costello syndrome complicated by cutis laxa, and to make a molecular genetic diagnosis. Methods Clinical data were collected from a case of Costello syndrome complicated by cutis laxa. Skin tissues were resected from the patient, and peripheral blood samples were obtained from the patient′s parents and 150 unrelated healthy controls. Genomic DNA was extracted from these samples, and all the exons and their flanking sequences of the HRAS gene were analyzed by DNA sequencing. Results The 13-month-old female patient presented with growth retardation, severe malnutrition, coarse facial appearance, severely loose skin over the limbs, and decrease or disappearance of subcutaneous fat. A heterozygous mutation c.34G > T （p.Gly12Cys） was detected in exon 2 of the HRAS gene in the patient, but not in her parents or 150 unrelated healthy controls. Conclusion The c. 34G > T （p.Gly12Cys） mutation in exon 2 of the HRAS gene may be responsible for Costello syndrome in the patient.