In-vivo dosimetry is an important technique to ensure accuracy of delivered dose during total body irradiation (TBI). We present an analysis of semiconductor diode dosimetry, constituting seven years of dosimetry data from eighty-six patients who underwent total body irradiation. For lateral field irradiation, the mean exit dose, averaged over five anatomical sites (head, sternal notch, chest, abdomen and pelvis) and as a percentage of the planned dose was 95.7% (SD 7.8%). For AP/PA irradiation, the mean exit dose averaged over five anatomical sites and as a percentage of the planned dose was 95.5% (SD 9.8%). We propose a number of possible reasons for these differences, including patient setup variations, movement of the patient and diodes during treatment, imprecise placement of planned bolus material, inaccurate inhomogeneity corrections and modelling by the treatment planning system.