Clindamycin is used to treat various bacterial infections, but its administration can cause anaphylaxis, liver reactions, pseudomembranous colitis, and peripheral blood cytopenias (anemia, neutropenia, and thrombocytopenia), alone or in combination. We report the case of a patient with a recurrent infection of the tonsils who received clindamycin. Pancytopenia, a previously unreported hematological disorder related to clindamycin use, was observed in conjunction with the infection and clindamycin treatment. One month prior to hospitalization, a 22-year-old man of Hispanic origin had a tonsillar infection and cough and began to have anal pain. These conditions became exacerbated three weeks later, coinciding with a new tonsillar infection, frequent nonproductive cough, and febrile syndrome. He received clindamycin for four days prior to his admission, without improvement. While hospitalized, he was found to have fever, tonsillar abscess, hemorrhoid thrombosis, and anal fissure; the latter was immediately resected under general anesthesia. Before surgery, our patient's blood count showed intense leukoneutropenia and mild thrombocytopenia that increased 12 hours later, along with the establishment of anemia. A bone marrow study showed decreased cell content, micromegakaryocytes, and an interruption of the differentiation of granulocytes and erythroblasts. Post-surgery, our patient received metronidazole, meropenem, and amikacin along with acetaminophen, ketoprofen, omeprazole, and pegfilgrastim, with resulting clinical and hematological improvement. Our experience with this patient establishes that well-documented clinical cases should be the basis for identifying and publicizing unknown or uncommon undesirable effects of drugs. We report that, in some individuals, clindamycin can cause pancytopenia, a complication that in our patient's case was caused by direct injury of his hematopoietic tissue.