We report on two sibs with partial 4q trisomy: dup (4)(q35.2-q31.22) and their renal biopsy findings. Both of them show renal hypoplasia, although their chromosomal aberration lacks the minimal duplicated region 4q22-q23 and/or 4q25-q31.3, which had been shown to be associated with urogenital abnormalities and thumb malformations in previous reports. From the renal biopsy findings, the two sibs were diagnosed as oligonephronia. We summarize the 13 having published cases of duplication of chromosome 4q, and examine which segments have a close relationship to renal hypoplasia. We suggest that renal hypoplasia may be female-prone, and may have a close relationship with duplication of 4q33-q34.