A retrospective investigation of Thoroughbred racehorses euthanazed as result of catastrophic musculoskeletal injury (CMI) at four racetracks in Gauteng, South Africa during the period of 1998-2004 was performed. Fifty-five cases of CMI from 103 603 starts were evaluated. The incidence of CMI per 1000 starts was 0.53, similar to the incidence reported worldwide. The affected limb of 32 of 55 horses with a CMI was evaluated radiographically, ultrasonographically and dissected. CMI occurred unilaterally and predominantly in the forelimbs, the left forelimb (LF) being most commonly affected. The suspensory apparatus, particularly the proximal sesamoid bones (PSB) was predominantly affected, mostly in the LF. Sixty-nine percent of the PSB fractures occurred biaxially, the medial PSB most commonly affected. PSB fractures were often associated with extensive damage to the flexor tendons and ligaments of the metacarpophalangeal joint. Lateral condylar fractures were more common than medial, and the right forelimb predominantly affected. Significant risk factors for CMI in this study were gender, racing interval, and weight carried. Gender relative to the number of starts had the highest statistical significance (intact males P<0.001 and geldings P=0.010). Intact males were 14.8 times more at risk than females and 5.3 times moreso than geldings. Horses carrying more than 59kg were 3.3 times more at risk of breakdown than horses carrying 54-59kg of weight (P=0.006). Horses with a racing interval of less than one week were approximately three times more at risk than those with longer intervals (P=0.025 and P=0.029 respectively). Statistically insignificant risk factors were racing year, going, distance, racetrack, age, size of field and draw. It is of paramount importance that CMI is strictly monitored and risk factors identified to implement preventative measures to circumvent occurrence of CMI, which may have a negative impact on this important spectator sport. This study provides benchmarks for the racing industry to monitor racetrack fatalities in Gauteng and to evaluate intervention strategies. Copyright / Dissertation (MMedVet)--University of Pretoria, 2009. / Companion Animal Clinical Studies / unrestricted