We aimed to describe associations between diet quality in adolescence and adulthood and knee symptoms in adulthood. Two hundred seventy-five participants had adolescent diet measurements, 399 had adult diet measurements and 240 had diet measurements in both time points. Diet quality was assessed by Dietary Guidelines Index (DGI), reflecting adherence to Australian Dietary Guidelines. Knee symptoms were collected using Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Data were analysed using zero-inflated negative binomial regressions. The overall adolescent DGI was not associated with adult knee symptoms, although lower intake of discretionary foods (e.g. cream, alcohol, bacon and cake) in adolescence was associated with lower pain (mean ratio (MR) 0·96) and dysfunction (MR 0·94). The overall adult DGI was not associated with knee symptoms; however, limiting saturated fat was associated with lower WOMAC (Pain: MR 0·93; stiffness: MR 0·93; dysfunction: MR 0·91), drinking water was associated with lower stiffness (MR 0·90) and fruit intake was associated with lower dysfunction (MR 0·90). Higher DGI for dairy products in adulthood was associated with higher WOMAC (Pain: MR 1·07; stiffness: MR 1·13; dysfunction: MR 1·11). Additionally, the score increases from adolescence to adulthood were not associated with adult knee symptoms, except for associations between score increase in limiting saturated fat and lower stiffness (MR 0·89) and between score increase in fruit intake and lower dysfunction (MR 0·92). In conclusion, the overall diet quality in adolescence and adulthood was not associated with knee symptoms in adulthood. However, some diet components may affect later knee symptoms.