18p deletion syndrome can be easily missed in a clinical setting as the facial features, though typical, can be overlooked and the other features including growth retardation and learning disability are nonspecific. We present a family in which the proband has 18p deletion syndrome. The proband performed better on verbal skills than on performance tasks on intelligence testing. She had attention-deficit hyperactivity disorder, which required medication and behavioral therapy. Subsequent cytogenetic analysis in her elder brother who presented with learning difficulties showed partial trisomy 18p and the maternal karyotype is 46, XX,(15;18)(p11.2;p11.2). This is the first report of a family with a balanced maternal translocation resulting in 18p deletion in one sibling and 18p partial trisomy in the other.