1. Two experiments were conducted to determine the effect of slaughter weight on the incidence and intensity of deep pectoral myopathy (DPM) of M. pectoralis minor (p. minor muscle) in commercial conditions in Turkey and to evaluate the impact of DPM on meat quality traits of pectoralis major (p. major) muscle in broilers.2. In Experiment 1, a total of 116 250 carcasses from 59 Ross-308 broiler flocks, classified according to slaughter weight as 2.0-2.2, 2.2-2.4, 2.4-2.6 and >2.6kg, were evaluated for occurrence of DPM. In Experiment 2, p. major samples from unaffected broilers and each DPM stage were evaluated for meat quality, oxidant and antioxidant properties, nutritional value and fatty acid profile. DPM was characterised as 1: muscles with coagulative necrosis, 2: muscles with fibrous tissue texture and pink to plumb and 3: muscles with green necrotic area.3. The average incidence of DPM was found to be 0.73% in Experiment 1 and independent of slaughter weight.4. In Experiment 2, p. major muscle of broilers with DPM 1 and 2had higher pH values with higher redness and drip loss. All DPM stages resulted in an increase in lipid content and malondialdehyde activity and lowered ash content of p. major muscle compared with unaffected birds. DPM 2 increased superoxide dismutase and glutathione peroxidase activities in M. p. major. The p. major of broilers with DPM had lower content of C18:2 conjugated linoleic and C20:3n-6 fatty acids than those of unaffected broilers. Lower 6 desaturase and thiosterase activities and 18:2n-6 to 18:3n-3 ratio were observed for all DPM stages compared to unaffected.5. It was concluded that these changes obtained in p. major muscle of broilers with DPM might indicate biochemical characteristics of muscle degenerations.