BACKGROUND: In the light of the new diagnostic criteria for multiple sclerosis (MS) and currently available early treatment, this study aimed to explore whether, and to what extent, disclosure of the diagnosis of MS or clinically isolated syndrome (CIS) affects patients' anxiety, mood and quality of life (QoL). METHODS: Eligible participants were all patients referred for the first time to the Neurological Unit who had manifested symptoms suggestive of MS for no more than 6 months. All patients were evaluated for (i) QoL (SEIQoL and MS-QoL54), (ii) Anxiety (STAI) and Depression (CMDI) on study inclusion (T0), 30 days after diagnosis disclosure (T30), and after 1 (T1y) and 2 (T2y) years' follow-up. RESULTS: Two hundred and twenty-nine patients were enrolled; 93 of these were unaware of their diagnosis. Patients who already knew their diagnosis (100 with CIS and 22 with MS) were excluded from the main analyses and used to perform control analyses. At the end of the screening, an MS diagnosis was disclosed to 18 of the 93 patients, whereas a CIS diagnosis was disclosed to 62 patients (12 patients received a diagnosis other than MS or CIS). Thirty days after diagnosis disclosure, irrespective of the diagnosis disclosed, both QoL and Anxiety and Depression were significantly rated as better compared to the start of screening, (p(s) < 0.03), and this improvement remained stable over the two annual follow-ups. However, as suggested by a significant 'Time' × 'Diagnosis' interaction with regard to both QoL and Anxiety and Depression (p(s) < 0.02), the effect of the disclosure in the short term differed depending on CIS or MS diagnosis. Specifically, on MSQoL, which is a health-related QoL scale, we found a statically significant improvement, immediately after the diagnosis disclosure, in both the MS and CIS groups (p(s) < 0.01). Differently, on SEIQoL, which is a non health-related QoL measure, and on the anxiety scale, we observed a statistically significant improvement only in the group which received a MS diagnosis (p(s) < 0.03). CONCLUSIONS: This first prospective study provides objective data showing that early disclosure of MS diagnosis improves both the patient's QoL and psychological well-being. In addition, the results seem to suggest that CIS disclosure does not lead to the same favourable effects.