Specific anatomy of the porcine stomach results in a high risk of ulceration in the pars oesophagea. A fully developed ulcer leads to intermittent gastrointestinal bleeding followed by clinical symptoms of chronic pain; thus, gastric ulceration in pigs causes significant production losses and serious welfare problems. Nowadays, gastric ulceration is common in domestic pigs throughout the world, but a great deal of attention has been directed at finishers. This paper was intended to provide new data on the prevalence of the disease in commercially reared highly prolific sows. The study was carried out on 329 culled sows from four commercial farms located in Northern Poland. The severity of gross pathological lesions of pars oesophagea was assigned to grade 0 (no lesions), 1 (parakeratosis), 2 (erosion), or 3 (gastric ulceration with or without stenosis) by a veterinary practitioner. Abattoir analysis revealed 66.6% of sows’ stomachs with some degree of alterations. Gastric ulceration was detected in 45.5% of examined organs. Parakeratosis and erosion were found in 1.2 and 15.8% of stomachs, respectively. The investigation did not find any oesphageal strictures. Our investigation of the problem in high health status hyper-prolific sows showed the lowest prevalence of gastric lesions (i.e., ulcerative and preulcerative alterations collectively) compared to earlier studies but the highest percentage of gastric ulcers. The results indicate that gastric ulcers may be a highly prevalent and underestimated welfare issue in sows in modern pig production, worth further studies focusing on particular risk factors related to feeding, genetics, management issues, and sows longevity.