Between November 1985 and June 1990 we performed 400 first trimester chorionic villi samplings (CVS). In the first 107 cases only transcervical CVS was performed, regardless of placental location. Later, 163 transcervical and 130 transabdominal CVS were performed, depending on placental location. Anterior and fundal placentas were approached transabdominally and posterior placentas transcervically. Multiple pregnancies were excluded. Successful results were obtained in 394 out of 400 cases. There were 5 failures in the first set of cases and 1 in the second (p < 0.05). In 14 cases (3.5%) fetuses with normal karyotypes were spontaneously aborted, 5 of these in the first period (4.7%) and 9 (3.1%) in the second. The spontaneous abortions in the second period followed transabdominal CVS in 4 cases out of 130 (3.1%) and the transcervical route in 5 cases out of 163 (3.105%). The average attempts per case in the first period was 1.44 (SD 0.66) while in the second it was 1.17 (SD 0.44, p < 0.0001) for the transcervical route and 1.06 (SD 0.2, p < 0.002) for the transabdominal route. In our experience choosing between transabdominal and transcervical CVS according to placental location is preferable to the sole use of transcervical CVS in terms of lower failure rate and fewer attempts per case. Proficiency in both techniques is mandatory for optimal results.