Four Natural Diamond Detectors (NDD) have been used for deuterium - tritium neutron spectrometry and flux monitoring during the 1997 tritium experiments (DTE1) carried out in the Joint European Torus (JET). Neutron energy spectra have been measured with three NDDs for discharge scenarios that included: (a) hot ion H-mode studies using combined NB and ICRF heating, (b) optimized shear experiments using combined NB and ICRF heating, (c) alpha - particles heating experiments with NB heating only and (d) ICRF heating studies without NB heating. Within the statistical accuracy of the data, the spectra for high performance discharges can be adequately represented by Gaussian distributions, whose fwhm values provide effective ion temperatures that characterize the energy distributions of the ions taking part in fusion reactions. The performance of the miniature diamond detectors for neutron spectrometry is evaluated through comparison with the results obtained from the major d-t neutron spectrometers installed at JET.