BACKGROUND: Severe atopic keratoconjunctivitis (AKC) is a relatively rare disease, and some cases are refractory to conventional steroid treatment. OBJECTIVE: To examine the efficacy of 0.1% tacrolimus ophthalmic suspension in treating severe AKC during a 1-year follow-up. METHODS: This was a single-center, retrospective clinical study. Sixty eyes from 30 patients with severe AKC who were treated with 0.1% tacrolimus ophthalmic suspension 4 times per day, were included. The mean age of the patients was 21.5 ± 13.7 years. The severity of objective signs was observed at baseline (before treatment), at 2 weeks, and at 1, 2, 3, 6, and 12 months after treatment initiation. Ten objective signs of palpebral conjunctiva, bulbar conjunctiva, limbus, and cornea were assessed using 4 grades (0 = normal; 1+ = mild; 2+ = moderate; 3+ = severe). Safety was assessed based on the incidence and the severity of adverse events. RESULTS: The total score of the 10 clinical signs significantly decreased from baseline 2 weeks after initiating tacrolimus eye drop treatment, except at 2 months. The mean total score of clinical signs was 13.6 ± 6.6 at the beginning of treatment, and decreased to 5.4 ± 4.8 12 months after initiation. Treatment was gradually tapered, with increasing intervals between applications. Additional medications were required to provide relief in 18 patients during follow-up. No patient discontinued treatment due to adverse drug effects. Herpes keratitis was observed in 3 cases during follow-up. However, these cases were completely controlled. CONCLUSION: The 0.1% tacrolimus ophthalmic suspension is effective for the treatment of severe AKC refractory to standard conventional treatments throughout a full year.