To clarify the conflicting recommendations for care of blowout fracture (BOF), a prospective randomized study is required. Here, we present a prospective randomized pilot study on BOF. This article aimed to evaluate which computed tomography (CT) findings predict late functional and/or cosmetic symptoms in BOF patients with ≥ 1.0 mL herniation of orbital content into maxillary and/or ethmoidal sinuses. It also aimed to evaluate which patients with BOF would benefit from surgical treatment or observational follow-up. Twenty-six patients with BOF ≥ 1.0 mL herniation were randomized to observational ( n  = 10) or surgical treatments ( n  = 16) and were followed up for functional and cosmetic symptoms for at least 1 year. The results from CT scan measurements were correlated to the patients' symptoms and clinical findings which we report in this pilot study. Of the 10 patients randomized to observation, five had an inferomedial BOF with a herniation of ≥ 1.3 mL and all patients developed cosmetic deformities and required surgery. The remaining five patients in the observational group had inferior BOF and one of them had a distance of 3.3 cm from the inferior orbital rim to the posterior edge of the fracture and developed a cosmetic deformity but was unwilling to proceed to surgical treatment, and four patients had a median distance of 2.9 cm from the inferior orbital rim to the posterior edge of the fracture and did not develop cosmetic deformities. The median time from injury to surgery was 13 (3-17) days for the surgical group and 37 (17-170) days for the patients who underwent surgery in the observational group. The surgical results were similar for all the operated patients at the final control. Diplopia decreased and remained partly in one patient in the surgical group and in two patients in the observational group. Hypoesthesia of the infraorbital nerve decreased in nonsurgically treated patients, but surgery seemed to induce hypoesthesia. In this prospective randomized controlled pilot study on BOF, all patients in the observational group with inferomedial fractures developed visible deformity. Diplopia in BOF, without ocular motility limitation, is believed to be due to edema. Diplopia is not an indication for surgery as long as it reduces over time.