PURPOSE: To present the case of a follicular lymphoma with the primary site in the left tonsil. CASE REPORT: A 47-year-old white woman lawyer presented on December 1, 2012 with a slight swelling in the left tonsil associated with difficulty in swallowing. The patient denied smoking, alcohol usage, or a history of tonsillitis, dysphagia, and odynophagia. She had no pain or fever, no palpable lymph nodes on examination of the neck, and. no other noted abnormality for the rest of the physical examination. Over the next 2 weeks, her symptoms continued to deteriorate. The patient was referred to the otorhinolaryngology service at Sao Jose do Avai Hospital. Fiberoscopy revealed tonsillar asymmetry with enlargement of the left tonsil. The tonsillar mucosa was firm and and fixed. There was no change on the right side. The patient was referred for surgery, and on January 4, 2013 a bilateral tonsillectomy was performed without complications. The surgical specimen was sent for histopathology and immunohistochemical analysis, which confirmed a Grade 3a follicular lymphoma in the left tonsil; the right tonsil had no lesion. Improvement in the patient's dysphagia was noted during the first postoperative examination. The patient was referred to the oncology service and was undergoing chemotherapy at the time of this report. CONCLUSION: Tonsillar asymmetry may be a sign of risk of malignancy, and a careful physical examination is extremely important for early diagnosis. Tonsils are involved in 80% of cases with non-Hodgkin's lymphoma that affect Waldeyer's ring. Tonsillectomy should be recommended whenever malignancy is suspected.