Papillary renal cell carcinoma (PRCC) is a malignant tumour arising from the renal tubular epithelium, representing 10–15% of renal cell carcinomas, with a male predominance. It may present with paraneoplastic symptoms, including constitutional syndrome in one-third of patients, typically fever, weight loss, and nausea. These manifestations are mediated by cytokines such as IL‑1, interferons, and prostaglandins, which may also contribute to diarrhoea, flushing, and fever.A 47‑year‑old man with type 1 diabetes mellitus presented to Primary Care with one week of non‑bloody diarrhoea. Stool cultures excluded infection. He subsequently developed constitutional symptoms, including unintentional weight loss of 10 kg, disproportionate to stool frequency. Laboratory tests revealed hypoproteinemia, and he developed bilateral lower limb oedema, asthenia, and bendopnea. He was admitted to Gastroenterology. CT imaging identified a mass in the upper pole of the left kidney, and a renal tumorectomy was performed. Histopathology confirmed papillary renal cell carcinoma (pT1a Nx Mx). Strengths included close follow‑up in Primary Care, enabling early recognition of red‑flag signs and timely referral. Limitations involved prolonged waiting times for other specialist consultations and diagnostic procedures, which delayed definitive diagnosis.Chronic diarrhoea in a patient with type 1 diabetes typically suggests autoimmune gastrointestinal disease. In this case, however, diarrhoea was a paraneoplastic manifestation of PRCC. Literature describes such syndromes but they remain rare and difficult to recognize in routine practice.This case underscores the importance of considering paraneoplastic syndromes in atypical presentations, maintaining vigilance for red‑flag symptoms, and strengthening coordination between Primary Care and hospital services to avoid diagnostic delays.PRCC accounts for 15% of renal cell carcinomas and occurs more frequently in men. Epidemiologic studies suggest increased cancer risk in patients with diabetes, including kidney malignancies, though evidence specific to type 1 diabetes and PRCC remains limited.This case highlights the critical role of family physicians in detecting atypical presentations, maintaining broad differentials, and ensuring effective communication across specialties to improve patient outcomes.