Introduction Depression and anxiety are common among patients with multiple sclerosis (MS) and are frequently present at the time of MS diagnosis. Methods POSIDONIA was a 12-month, observational, prospective study conducted in Italy to evaluate the impact of disease-modifying treatment (DMT) on emotional burden in patients with recently-diagnosed MS. The Hospital Anxiety and Depression Scale (HADS), specifically HADS anxiety (HADS-A) and depression (HADS-D) subscale scores, the Short-Form 36 Health Survey (SF-36) and the Impact of Event Scale - Revised (IES-R) were used to measure patient-reported outcomes. The Hamilton Depression Rating Scale (HDRS), HDRS-17, was used as a measure of healthcare provider-reported outcomes. The primary study outcome was change from baseline in feelings of anxiety and depression over 12 months (via HADS). Results Of 250 enrolled patients, 222 (88.8%) completed the study. At baseline, mean HADS total, HADS-A and HADS-D subscale scores were within the normal range. There were no significant changes over time in mean HADS total and HADS-A and HADS-D subscale scores, although the subgroup of patients with baseline scores indicative of anxiety or depression tended to improve over time. Both the HDRS and IES-R total scores improved over time, but there were no statistically significant changes in SF-36. Conclusion In the patient population of the POSIDONIA study depression and anxiety were present in a minority of patients thus not allowing to detect the impact of starting DMT. However DMT appears to have a positive effect in patients with measurable anxiety or depression at baseline.