Introduction and objective: Evaluation of subclinical inflammation in patients with primary hypertension (PH) and white coat hypertension (WCH). Materials and methods: In 56 untreated paediatric patients with PH, 40 with WCH, and 30 healthy individuals (control group, CG), we evaluated high sensitivity C-reactive protein (hsCRP), interleukin 18 (IL-18) levels, complete blood count-derived markers of inflammation, office and ambulatory blood pressure, and selected clinical and biochemical parameters. Results: hsCRP was significantly higher in PH patients compared to CG, and neutrophil and monocyte counts were significantly higher in PH and WCH patients compared to CG. Receiver operating characteristic analysis revealed good prognostic profiles for hsCRP, neutrophil, lymphocyte, monocyte, and platelet counts, as well as neutrophil-to-lymphocyte ratio (NLR), monocyte-to-neutrophil ratio, and platelet-to-mean platelet volume ratio as predictors of the presence of PH. In multivariate analysis, monocyte-to-lymphocyte ratio (MLR) and platelet count (β = 0.217, β = 0.191) were significant predictors of office diastolic blood pressure Z-score, while neutrophil count predicted 24 h systolic blood pressure Z-score (β = 0.365), MLR, lymphocyte count, IL-18, and NLR predicted 24 h diastolic blood pressure Z-score (β = 0.305, β = 0.253, β = −0.197, β = −0.189), and neutrophil count together with IL-18 predicted 24 h mean arterial pressure Z-score (β = 0.210, β = −0.209). Conclusions: 1. Patients with PH and WCH are characterised by similar levels of subclinical inflammation, which are significantly higher compared to healthy peers. 2. Complete blood count-derived indices, especially neutrophil count and MLR, can serve as important adjuncts to the clinical evaluation of paediatric patients with PH.