A sample of 104 lamb and mutton carcases was selected on the market at an abattoir in three age groups and four mass classes representing five of the six fat classes of the classification system. The loin cut of the left side was used to evaluate the organoleptic characteristics. The M. longissimus thoracis was dissected from the left side to study the influence of age, carcase mass and fatness on collagen solubility, total collagen and pigment content of the muscle. As the age of lamb/sheep increased a decline was observed in the tenderness, juiciness, flavour, residue and collagen solubility of the meat. Results from a growth experiment indicated that after 4 months of age there was a marked decline in muscle collagen solubility. Carcase fatness was found to have an influence on certain meat quality characteristics and should not be ignored completely in a classification system. The influence of carcase mass on meat quality was in most instances negligible. As age of the animal plays such a predominany role on meat quality characteristics, age should be included as a parameter in any carcase classification or grading system. The current age grouping in the classification system should therefore remain unchanged, namely 0 tooth, 1 – 6 tooth and more than 6 tooth.