Abstract Objective: We recently demonstrated efficacy of intranasal theophylline in treatment of hyposmia in a large, diverse group of patients who exhibited this abnormality over an extended time period. Because hyposmia is long lasting we wished to evaluate hyposmia severity among patients related to length of time they exhibited hyposmia prior to initial evaluation and to whether hyposmia length or severity influenced treatment efficacy. Methods: Ninety-four patients with hyposmia were studied. Thirty-two had hyposmia for < 12 months prior to treatment whereas 62 had hyposmia >12 months before treatment. Treatment was intranasal delivery of 20 µg theophylline twice into each nostril once daily for two-12 months. Subjective responses, olfactometry and gustometry were obtained before and after treatment. Results: Hyposmia was similar in severity degree in both patient groups whether they exhibited hyposmia < or > 12 months after hyposmia onset. However, treatment with intranasal theophylline resulted in greater improvement in patients with onset < 12 months. Conclusions: Whereas degree of hyposmia severity does not differ with respect to length of dysfunction prior to treatment, treatment with intranasal theophylline was more effective in patients who exhibited hyposmia for shorter time periods - the earlier the treatment the better the result.