Purpose <p>Hematological parameters obtained from a pretreatment peripheral blood lab test, as well as indices calculated from these parameters, are associated with the prognosis of the disease in patients with head and neck squamous cell carcinomas (HNSCC). The aim of this study is to determine which of the parameters or indices would have the best prognostic ability in HNSCC patients treated with chemo-radiotherapy or bio-radiotherapy.</p> Methods/patients <p>Retrospective study of 345 patients with HNSCC treated with chemo/bio-radiotherapy, for whom a pretreatment lab test was available.</p> Results <p>Of the parameters and indices analyzed, the one with the best prognostic capacity was the Host-index (H-index), which combines the prognostic capacity of hemoglobin and albumin levels, along with the absolute counts of neutrophils, monocytes, and lymphocytes. This index was available for 309 patients. Based on a recursive partitioning analysis, three groups of patients were defined according to the H-index. Considering as reference the patients with an H-index lower than 1.88 (<i>n</i> = 80, 25.9%), patients with an H-index value between 1.88 and 3.62 (<i>n</i> = 115, 37.2%) had a 2.74 times higher risk of dying due to the tumor (95% CI 1.41–5.30, <i>P</i> = 0.003), and patients with an H-index value greater than 3.62 (<i>n</i> = 114, 36.9%) had a 5.62 times higher risk (95% CI 2.95–10.81, <i>P</i> = 0.0001).</p> Conclusion <p>The index derived from peripheral blood parameters that showed the best prognostic capacity in patients with head and neck squamous cell carcinoma treated with chemo/bio-radiotherapy was the H-index.</p>