Fetal arm, leg, and foot lengths were freshly measured with vernier calipers on all fetuses aborted by me from 1975 to 1983. With the use of these measurements from the 575 patients with reliable menstrual or conception dates and uterine size in agreement (+/- 2 weeks) with dates, statistical analyses were performed to determine the polynomial regressions of menstrual weeks of pregnancy for each extremity length. The data best fit the following formulas, where W represents weeks and F, L, and A are foot, leg, and arm lengths in centimeters: W = 3.03 + 17.4(F) - 10.8 (F2) + 3.36(F3) - 0.367(F4); W = 5.74 + 6.49(L) - 1.90(L2) + 0.305(L3) - 0.0161(L4); W = 5.19 + 5.65(A) - 1.45(A2) + 0.203(A3) - 0.00934(A4). Mean foot lengths at each week agreed well with those of Streeter, and when corrected for bias, all foot lengths were in near perfect agreement with his data.