Multiple Sclerosis (MS) is a degenerative disease and a common cause of disability in adults. 85% of people with MS (pwMS) are initially diagnosed with relapsing remitting MS (RRMS), which involves discreet periods of relapses and remission of symptoms. Over time, most, but not all, pwMS transition to secondary progressive MS (SPMS), which is characterised by a gradual accumulation of disability. Little research to date has explored the experience of this transition. Nine pwMS and seven MS health professionals (HPs) were interviewed to explore pwMS' experiences, coping and needs during this transition. Four major themes were identified using Thematic Analysis (Braun & Clarke, 2006); 'is this really happening?', 'becoming a reality', 'a life of struggle', and 'brushing oneself off and moving on'. Findings suggest a process of moving from uncertainty towards confirmation of one's diagnostic label, the experience of which was influenced, in part, by the attitudes and approaches of HPs themselves. Understanding pwMS' experiences of the transition is essential if clinicians are to provide pwMS with appropriate support during the transition. Several possible implications for theory and practice were put forward.