?Rational, aims and objectives: The aim of this Vignette study was to assess whether physiotherapists (PTs) make reasoned adaptations to evidence-based treatment recommendations when co-morbidity influences single disease treatment. Method: To study the influence of co-morbidity on treatment recommendations, 3 vignettes were created based on authentic patient data. In the first vignette, a patient with a single-diseased Intermittent Claudication (IC) was described, in the second vignette, co-morbidity Chronic Obstructive Pulmonary Disease (COPD) was added. In the third vignette, Knee Osteoarthritis (OA) was additionally added. Therapists described 3 treatment plans and their decision rationale. A random selection of 100 Dutch Claudication Network members was invited to participate in this qualitative study. Results: The response rate was 61%. Thirty percent of the physical therapists did not adjust treatment despite co-morbidity. Another 30% partly adapted the treatment plan when co-morbidity was added to the vignette. The presence of co-morbidity induced 40% to abandon guideline recommendations and to create an individualised treatment plan based on the health needs of the vignette patient. Conclusion: This study showed that the majority of PTs makes adaptations to otherwise evidence-based recommendations when co-morbidity is present in order to tailor treatment to the specific needs of the individual patient. However, the same patient was treated in various ways by different PTs.