Ocular adnexal mucosa-associated lymphoid tissue lymphoma (OAML) has been recognized as most common primary orbital malignancy. However, little was known about the response criteria for OAML. Our aim was to suggest response criteria for nonconjunctival OAML; the response evaluation of which using the conventional response criteria is inappropriate. A retrospective chart review of 34 eyes from 30 patients diagnosed with nonconjunctival OAML was conducted, focusing on the change in tumor size based on linear bi-dimensional and three-dimensional methods in magnetic resonance imaging (MRI) of the orbit. The maximum tumor response period of each case was investigated, and the expected optimal response period was calculated using regression analysis. In 30 evaluable patients, the median time taken for the maximum tumor response was 6 months (range, 3-18). More than 75 % of patients attained maximal tumor response in 6 months after initial therapy for follow-up period, the median value of which was 30 months (range, 15-77). Based on the regression analysis, it took 4.7 months for the maximum diameter (2r) of tumor to decrease by 50 % of initial lesion size. We cautiously suggest that optimal response could be defined as 50 % reduction of the maximum diameter in 6 months since the treatment was initiated, and that only observation without additional therapy is enough for nonconjunctival OAML, if optimal response is achieved.