The sources of error in the determination of residual stresses using neutron diffraction arise both from normal experimental uncertainties and from some inherent uncertainties in the nature of the measurements themselves. This presentation is aimed at provoking discussion firstly of errors and uncertainties in strain determination including:- 1. Errors on peak and multi-peak analysis; 2. The effects of the Ikeda-Carpenter function on the errors in pulsed source measurements; 3. Thermal, grain size, texture and compositional effects; 4. Sampling volume uncertainties in strain tensor determination (vs strain sensitivity); 5. Problems in establishing the true “zero strain” condition.