Background: Identifying the transition from relapsing-remitting to secondary progressive multiple sclerosis (SPMS) can be challenging for clinicians. Little previous research has explored how professionals experience working with patients during this specific stage of the disease. We explored the experiences of a group of multidisciplinary professionals who support patients in the transition to SPMS to describe this stage from a professional perspective. Methods: This qualitative semistructured interview study included 11 professionals (medical, nursing, and allied health professionals; specialists and generalists) working with patients with MS in South Wales, United Kingdom. Thematic analysis of the interview data was performed. Results: Two overarching themes were identified: the transition and providing support. The transition theme comprised issues related to recognizing and communicating about SPMS. Uncertainty influenced recognizing the transition and knowing how to discuss it with patients. The providing support theme included descriptions of challenging aspects of patient care, providing support for caregivers, using the multidisciplinary team, and working within service constraints. Providing adequate psychological support and engaging patients with self-management approaches were seen as particularly challenging. Conclusions: Caring for patients in the transition to SPMS generates specific challenges for professionals. Further research on health-care interactions and patients'/professionals' experiences regarding the transition phase may help identify strategies for professional development and learning and how to optimize the patient experience at this difficult stage of disease.