Background In some orbital mass lesions, histology may be the only way to establish an accurate diagnosis. Core needle biopsy (CNB) is widely performed in oncology, and unlike fine needle aspiration biopsy (FNAB), it can provide sufficient tissue sample for histology and immunohistochemistry. The purpose of this study was to evaluate the usefulness and possible complications of CNB of orbital tumors. Methods Fifty orbital lesions from 46 patients (age: 2–84 years) were biopsied using 20-gauge and 18-gauge semi-automated needles; 11 procedures were performed under ultrasound guidance. All 50 samples received routine histopathological examination and immunohistochemical analysis. Results Specimens diagnostically sufficient for histological analysis were obtained in all biopsies. The histopathological diagnosis was established in 94 % of specimens: 30 tumors were malignant: lymphoma (20); rhabdomyosarcoma (six); lacrimal gland carcinoma (one); breast carcinoma metastasis (two); melanoma (one); three were benign; ten inflammatory; and four were orbital fibrosis. Three biopsies were nondiagnostic: two (lymphoma, angiofibroma) showed undetermined identification and one was a false-negative (lacrimal gland adenocarcinoma was misdiagnosed as fibrous tissue). The diagnoses were confirmed by excisional or incisional biopsy in 26 patients. The concordance rate in patients with a surgically confirmed diagnosis was 88 %. The sensitivity, specificity and accuracy for differentiating malignant from benign lesions were 94 %, 100 %, and 96 %, respectively. Two patients suffered complications: mild retrobulbar hematoma with no decreased visual acuity. There was no damage to the globe or optic nerve, motility disorder, or infection. Conclusions CNB of orbital mass lesions is a safe procedure that provides a sufficient amount of tissue for histology and immunohistochemistry, and may be useful for improving the quality of the pathological diagnosis of orbital tumors.