BACKGROUND: Dysregulated T lymphocyte response is thought to play a key role in chronic intestinal inflammation (CIE). OBJECTIVES: To evaluate the presence of changes in peripheral and intestinal T lymphocyte subsets and to describe potential immune and inflammatory biomarkers in dogs with CIE. ANIMALS: Sixteen healthy dogs and 26 dogs were diagnosed with CIE. METHODS: Prospective case-control study evaluating peripheral and intestinal T lymphocytes using flow cytometry and inflammatory markers obtained from complete blood cell counts. RESULTS: Dogs with CIE had higher peripheral activated T helper (Th) lymphocytes (87/μL [18-273] CIE, 44/μL [16-162] healthy control (HC, P = .013) and regulatory T cells (Treg; 108/μL [2-257] CIE, 34/μL [1-114] HC, P = .004). In the intestinal epithelium, CIE dogs presented lower percentages of Th (4.55% [1.75-18.67] CIE, 8.77% [3.79-25.03] HC, P = .002), activated Th cells (0.16% [0.02-0.83] CIE, 0.33% [0.05-0.57] HC, P = .03) and CD4/CD8 ratio (0.08 [0.02-0.39] CIE, 0.21 [0.07-0.85] HC, P = .003). Conversely, higher percentage of activated T cytotoxic cells (20.24% [3.12-77.12] CIE, 12.32% [1.21-39.22] HC, P = .04) and interferon-gamma (IFN-γ) producing T lymphocytes (7.36% [0.63-55.83] CIE, 1.44% [0.00-10.56] HC, P = .01) within the epithelium was observed. In the lamina propria the percentage of Treg lymphocytes was higher (6.02% [1.00-21.48] CIE, 3.52% [0.18-10.52] HC, P = .02). CONCLUSIONS AND CLINICAL IMPORTANCE: Systemic and intestinal immune alterations occur in dogs with CIE suggesting that blood IFN-γ producing T lymphocytes and the systemic immune-inflamation index (SII) could potentially serve as biomarkers for the disease.