Abstract Background Pheochromocytoma is associated with systemic inflammation, but the underlying mechanisms are unclear. Therefore, we investigated the relationship between plasma metanephrine levels and haematological parameters – as a surrogate of inflammation – in patients with pheochromocytoma and the influence of preoperative α-blockade treatment. Design and Methods We retrospectively studied 68 patients with pheochromocytoma who underwent adrenalectomy (median age 53 years, 64.7% females) and two control groups matched for age, sex, and body mass index (BMI): 68 patients with non-functioning adrenocortical tumors (NFAT) and 53 with essential hypertension (EAH). The complete blood count (CBC) and several inflammation-based scores [Neutrophil-to-Lymphocyte Ratio (NLR), Platelet-to-Lymphocyte Ratio (PLR), Lymphocyte-to-Monocyte Ratio (LMR), Systemic-Immune-Inflammation Index (SII), Prognostic-Nutrition Index (PNI)] were assessed in all patients and, in a subset of pheochromocytomas, after adrenalectomy (n=26) and before and after preoperative α-blockade treatment (n=29). Results A higher inflammatory state, as indicated by both CBC and inflammation-based scores, was observed in patients with pheochromocytoma compared to NFAT and EAH. Plasma metanephrine levels showed a positive correlation with NLR (r=0.4631), PLR (r=0.3174), SII (r=0.3709), and a negative correlation with LMR (r=0.4368) and PNI (r=0.3741), even after adjustment for age, sex, ethnicity, BMI and tumor size (except for PLR). After adrenalectomy, we observed a reduction in NLR (p=0.001), PLR (p=0.003), SII (p=0.004) and a concomitant increase in LMR (p=0.0002). Similarly, α-blockade treatment led to a reduction in NLR (p=0.007) and SII (p=0.03). Conclusions Inflammation-based scores in patients with pheochromocytoma showed pro-inflammatory changes that correlated with plasma metanephrine levels and are ameliorated by adrenalectomy and α-blockade.