The aim of this study was to investigate the reproducibility, reliability and accuracy of Mirels’s score in upper limb bony metastatic disease and validate its use in predicting pathological fractures. Methods 45 patients with upper limb bony metastases met the inclusion criteria (62% male 28/45). Mean age was 69 years (SD 9.5) and commonest primaries were lung (29% 13/45), followed by prostate and hematological (each 20% 9/45). The most commonly affected bone was the humerus (76% 35/45), followed by the ulna (6.5% 3/45). Mirels’s score was calculated in 32 patients; with plain radiographs at index presentation scored using Mirels’s system by 6 raters. The radiological aspects (lesion size and appearance) were scored twice by each rater (2-weeks apart). Intra- and interobserver reliability were calculated using Fleiss’ kappa test. Bland-Altman plots compared the variances of both individual components and total Mirels’s score. Results The overall fracture rate of upper limb metastatic lesions was 76% (35/46) with a mean follow-up of 3.6 years (range 11 months-6.8 years). Where time from diagnosis to fracture was known (n=20), fractures occurred at a median 19 days (IQR 60-10) and 80% (16/20) occurred within 3-months of diagnosis. Mirels’s score of ≥9 did not accurately predict lesions that fractured (fracture rate 11% 5/46 for Mirels’s ≥9 versus 65% 30/46 for Mirels’s ≤8, p