Background Patients with recurrent or metastatic head and neck squamous cell carcinoma (R/M-HNSCC) have a poor prognosis and limited therapeutic options. Immune checkpoint inhibitors (ICIs) are effective in patients with tumor progression < 6 months following first-line, platinum-based chemotherapy (PBC), but data are missing for patients with progression ≥ 6 months after the last platinum dose. Methods Retrospective analysis (six French centers, 2008–2019) of all consecutive R/M-HNSCC patients. treated first-line with PBC and tumor progression ≥ 6 months after the last platinum dose. Primary endpoint: progression-free survival after second-line therapy (PFS2). Additional endpoints: overall survival from Day 1 of first-line (OS1) and second-line (OS2) therapy. Results R/M-HNSCC patients (n = 144) received cisplatinum (n = 67, 47%) or carboplatinum (n = 77, 53%) first-line. Response after first-line: complete response (CR; n = 16, 11%); partial response (PR; n = 77, 53%); stable disease (n = 22, 15%). Second-line therapy: PBC (n = 95, 66%); platinum-free regimen (PFR) (n = 25, 17%); ICI (n = 24, 17%). Median [95% confidence interval] PFS (months): PBC 5.0 [3.8–6.2]; PFR 4.0 [1–7.0]; ICI 2.0 [0.4–3.6] (p = 0.16). For PBC, PFR, and ICI, respectively: OS1 30, 23, and 29 months (p = 1.02); OS2 14, 10, and 16 months (p = 0.25); PR, 26%, 16%, and 21% patients; CR, 0%, 8%, and 4% patients. For subsequent lines, ICIs were administered for PBC (n = 11, 12%) and PFR (n = 2, 8%). No predictive factor for efficacy (PFS, OS) was identified. Conclusions Our retrospective study suggests similar efficacy regarding OS2 for second-line chemotherapy or ICI in R/M-HNSCC patients with progression ≥ 6 months after the last first-line platinum dose.