Dietary intake has been shown to influence acid-base balance in human subjects under tightly controlled conditions. However, the net effect of food groups on alkali/acid loading in population groups is unclear. The aims of the present study were to: (1) quantify estimates of daily net endogenous acid production (NEAP) (mEq/d) in a representative group of British elderly aged 65 years and older; (2) compare and characterise NEAP by specific nutrients and food groups likely to influence dietary acid loading; (3) determine whether geographical location influenced NEAP. The National Diet and Nutrition Survey dataset, consisting of a 4 d weighed record and anthropometric data, was used to estimate dietary acidity. Dietary under-reporters were excluded by analysing only subjects with energy intakes >/= 1.2 x BMR. NEAP was estimated as the dietary potential renal acid load+organic acid excretion, the latter as a multiple of estimated body surface area. NEAP was lower in women compared with men (P < 0.001), and lower than values reported in a Swedish elderly cohort. Lower dietary acidity was significantly associated with higher consumption of fruit and potatoes and lower consumption of meat, bread and eggs (P < 0.02 to P < 0.001). Lower intakes of fish and cheese were associated with lower NEAP in men only (P < 0.01 to P < 0.001). There were regional differences for NEAP, with higher intakes in Scotland/Northern regions compared with Central/South-Western and London/South-Eastern regions (P = 0.01). These data provide an insight into the acid-generating potential of the diet in the British elderly population, which may have important consequences in this vulnerable group.