We present a case of isolated abducens nerve palsy with negative magnetic resonance imaging (MRI) findings and unusual cerebrospinal fluid results. The patient was treated for a central nervous system infection initially. After the second cerebrospinal fluid examination, a diagnosis of central nervous system leukemia was made. Isolated abducens nerve palsy is not always a stable or benign illness, even with a normal brain MRI study. Abnormal cerebrospinal fluid results should suggest the presence of a central nervous system malignancy.