Within 3 working days in September, 1974, we made three prenatal diagnoses of 47,XY, +21 from three women of advanced maternal age. Two were 37 and 38 years old, respectively, and nulliparous. One was 42 years old and had four normal children. The possibility of cell contamination arose when the second diagnosis of trisomy 21 and a male fetus was made. This suspicion increased when the third case was found within 3 working days. All three cases were then studied with both Q and G banding for identification of individual chromosome markers. Fortunately, the distinction was clear by Q‐banding. Each case showed characteristic Q‐banding polymorphisms in No. 3 and No. 21 chromosomes. It was evident that these were three separate cases. Problems relating to diagnosis of two or more successive identical trisomies of the same sex can be resolved by banding techniques. The response each family had to learning the diagnosis is presented and discussed.