Background Wolf-Hirschhorn syndrome (WHS) results from the partial deletion of 4p. This study aimed to identify and fine map the chromosome deletion regions of Chinese children with Wolf-Hirschhorn syndrome among the developmental delay/mental retardation (DD/MR) patients. Methods We analyzed the relationship of phenotype and genotype. Inclusion criteria were: moderate to severe DD/MR, no definite perinatal brain injury, and no trauma, toxication, hypoxia, infection of central nervous system; routine karyotyping was normal, no evidence of typical inherited metabolic disorder or specific neurodegenerative disorders from cranial neuro-imaging and blood/urinary metabolic diseases screening; no mutation of FMR1 in male patients, no typical clinical manifestation of Rett syndrome in female patients. Multiplex ligation-dependent probe amplification (MLPA) and Affymetrix genome-wide human SNP array 6.0 assays were applied to accurately define the exact size of subtelomeric aberration region of four WHS patients. Results All four WHS patients presented with severe DD, hypotonia and microcephaly, failure to thrive, 3/4 patients with typical facial features and seizures, 2/4 patients with congenital heart defects and cleft lip/palate, 1/4 patients with other malformations. The length of the deletions ranged from 3.3 Mb to 9.8 Mb. Two of four patients had "classic" WHS, 1/4 patients had "mild"-to-"classic" WHS, and 1/4 patients had "mild" WHS. Conclusions WHS patients in China appear to be consistent with those previously reported. The prevalence of signs and symptoms, distribution of cases between "mild" and "classic" WHS, and the correlation between length of deletion and severity of disease of these patients were all similar to those of the patients from other populations. Chin Med J 2010;123(13):1663-1667