Partial trisomy of the long arm of chromosome 1 is a relatively rare cytogenetic anomaly. Its phenotype has still not been completely defined, because of the cytogenetic heterogeneity of the cases so far described. We report a prenatal case of partial 1q trisomy associated with partial monosomy 4q, secondary to balanced maternal translocation t(1;4). The trisomic segment extended from 1q31.1 to qter and the monosomy 4q was from 4q35.2 to qter. The phenotypic anomalies found by post‐mortem and autopsy examinations were compared with those of similar cases reported in the literature. We performed standard cytogenetics and fluorescence in situ hybridization. Cerebral ventriculomegaly, present in our case, seemed to be a constant feature in partial 1q trisomies, so this cerebral malformation could be considered as the main echographic marker for this chromosomal imbalance and trisomy 1q should be added to the list of chromosomal abnormalities associated with ventriculomegaly.