Multiple sclerosis (MS) is an immune-mediated demyelinating disorder involving the central nervous system (CNS). It is common amongst young females. Although the exact cause of MS is yet unknown, viral infections such as EBV, environmental factors, and autoimmune and genetic mechanisms involving HLA-DRB1 loci are implicated. Familial MS is reported from some geographic locations and ethnic groups but is thought to be rare in Asia. In this paper, we present both a Sri Lankan mother and her son, with clinically definite MS conforming to McDonald's 2017 clinical and MAGNIMS 2016 radiological criteria. Both had oligoclonal bands in their CSF (OCB-IEF) with no serum bands indicating intrathecal production and were negative for AQP4 and MOG IgG serology. Familial MS is more common among siblings, with sister-sister relationship having the highest rate. The lowest relation was amongst father-son and mother-son pairs. Amongst siblings, the risk of MS is between 3.5% and 4.7%. Inherited factors rather than common environmental exposure influence susceptibility in such cases. To the best of our knowledge, MS occurring in a mother-son pair has not been reported before either from Sri Lanka or South Asia.