Depending on the season, the etiologies of hypersensitivity pneumonitis (HP) tend to vary. To investigate the clinical characteristics of winter-onset acute hypersensitivity pneumonitis (W-AHP), we compared 13 cases of W-AHP with 19 cases of summer-onset acute hypersensitivity pneumonitis (S-AHP). We retrospectively examined their pathogenesis, clinicoradiological findings, and presence or absence of recurrence after antigen avoidance. The causes that led to HP were as follows: six cases of ventilator-associated HP; three cases of home-associated HP (including summer-type HP); two cases of bird-related HP, and two cases of hot tub lung. There was a higher proportion of men among the W-AHP patients than women, and the mean age of the patients’ houses was lower in that group than among S-AHP patients. Lastly, no recurrence was observed in patients who achieved total antigen exposure avoidance.