Objectives: To analyse the relationship between spirometric parameters measured with a face mask versus a mouthpiece, as well as the feasibility of face mask spirometric evaluation in a head and neck surgery (HNS) decannulation context. Furthermore, we examine peak inspiratory flow (PIF) cut-off values before and after decannulation. Design: Prospective cohort study. Setting: Otolaryngology HNS Department of a university teaching hospital. Participants: Twenty-four patients were selected. A maximal flow-volume loop was conducted before (with mouthpiece) and after (with mouthpiece and face mask) decannulation. Main outcome measures: Recorded outcomes were forced vital capacity (FVC), forced expiratory volume in the first second, peak expiratory flow, PIF, forced expiratory flow at 50% of FVC and forced inspiratory flow at 50% of FVC. Spearman correlation coefficients between spirometric parameters measured with a face mask versus a mouthpiece were calculated. Wilcoxon test was used to check differences between mouthpiece and face mask values. Results: Correlation between mouthpiece and face mask spirometric values was moderate to high (r = 0.46-0.95). All parameters measured by spirometry were significantly lower with a face mask than those obtained with a mouthpiece (p < 0.05). Before decannulation, the lowest PIF value (tested with mouthpiece) that allowed successful decannulation was 1 L/s. After decannulation, the lowest PIF value tested with mouthpiece and face mask for successful completion of the decannulation process were 0.77 and 0.56 L/s, respectively. Conclusion: Face mask is a feasible option to perform a spirometry when face diseases hinder spirometric evaluation through a mouthpiece in an HNC surgery context.