Infection with human T cell lymphotropic virus type 1 (HTLV-1) is in most cases indolent; however, some patients develop adult T cell leukemia, associated with poor prognosis, or the highly disabling and incurable HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) (Verdonck et al. 2007; Cooper et al. 2009). HTLV-1 is an endemic infection in Southern Japan, Iran, South America, the Caribbean basin, West Africa, and among aborigines in Australia (Verdonck et al. 2007). There are no established biomarkers to predict complications in HTLV-1; however, the percentage of peripheral blood mononuclear cells (PBMCs) harboring the provirus, called proviral load (PVL), and beta-2 microglobulin (β2M) in serum are surrogate biomarkers. Associations with neurological syndromes other than HAM/TSP have been claimed, including neuropathy, motor neuron disease (Araujo et al. 2019), as well as cerebellar ataxia (Iwasaki 4,5,6,; Kira et al. 1993; Gracia et al. 1995; e-1 to e-6). In the majority of reported cases, ataxia occurred in Japanese patients with HAM/TSP (Iwasaki 1990; Iwanaga 1993; Kira et al. 1993; e1, e-2, e-4, e-6). Here, we present an Iranian HTLV-1 positive patient with a cerebellar syndrome, elevated β2M in serum, and elevated neopterin and CXCL10 in cerebrospinal fluid (CSF).