Purpose: Increasing knowledge suggests that nutrition and lifestyle factors affect multiple sclerosis. This study explores how people with multiple sclerosis experience daily multiple sclerosis disease activity and the influence of nutrition and lifestyle factors (e.g., stress, sleep, and environmental temperature). Methods: Four phases mix qualitative and quantitative elements in an exploratory study. The initial two phases consisted of an exploratory study with 14 participants followed by 15 semi-structured interviews. Results from the two first phases were substantiated in a survey completed by 425 respondents (response rate: 42.5%). Finally, findings and inconsistencies were elaborated in three focus group interviews. Results: In the initial exploratory study, several of the participants linked nutrition and lifestyle factors to disease activity. Results from the semi-structured interviews showed that particularly stress, meat, fatty foods, and processed sugar were perceived to have a negative impact on disease activity, and some participants had experienced immediate effects of these factors on their disease activity. The survey supported these findings that were further elaborated in focus groups. Conclusion: People with multiple sclerosis perceive nutrition and lifestyle to affect daily disease activity. Individuals who have experienced links between their multiple sclerosis, and nutrition and lifestyle attribute some of these changes to e.g., stress, and the consumption of sugar, meat, and fatty food.