Relative differential cross-sections for the excitation of vibrational levels of HI up to upsilon = 8 by slow electron impact have been measured as a function of the incident electron energy in the range 0-3 eV. The results confirm the shapes of the theoretical cross-sections of Domcke and Nakamura [Z. Phys. D 42 (1997) 181], in particular the prediction that no threshold peaks are found in HI, in contrast to the lighter hydrogen halides. The spectra up to upsilon = 0 --> 6 have structures at vibrational thresholds, in agreement with the theoretical predictions.