A new set of determinations of the decay constant for spontaneous fission of 238U, λf, using mica-uranium sandwich and thin films of natural uranium is presented. A value of λf = (8.37±0.17) × 10-17 a-1 has been determined. The use of uranium-based neutron dosimetry for the measurement of λf through fission-track techniques is discussed. Particularly, the λf measurement by Roberts et al. (Phys. Rev. 174 (1968) 4847), is analyzed, showing that the value obtained by these authors (7.03 × 10-17 a-1) underestimated λf. It is concluded that the dosimetry based on U(n,f) reaction does not support a λf value around 7 × 10-17 a-1 determined by various authors using mica-uranium sandwich. © 2002 Elsevier Science B.V. All rights reserved.