Abstract Background The aims of this study were: to investigate the capacity of the rare disease healthcare network in Campania to diagnose patients with rare diseases during the outbreak of Covid-19; and to shed light on problematic diagnoses during this period. Methods To describe the impact of the Covid-19 pandemic on the diagnosis of patients with rare diseases, a retrospective analysis of the Campania Region Rare Disease Registry was performed. A tailored questionnaire was sent to rare disease experts to investigate major issues during the emergency period. Results Prevalence of new diagnoses of rare disease in March and April 2020 was significantly lower than in 2019 (117 versus 317, P < 0.001 and 37 versus 349, P < 0.001, respectively) and 2018 (117 versus 389, P < 0.001 and 37 versus 282, P < 0.001, respectively). Eighty-two among 98 rare disease experts completed the questionnaire. Diagnostic success (95%), access to diagnosis (80%) and follow-up (72%), lack of Personal Protective Equipment (60%), lack of Covid-19 guidelines (50%) and the need for home therapy (78%) were the most important issues raised during Covid-19 outbreak. Conclusions This study describes the effects of the Covid-19 outbreak on the diagnosis of rare disease in a single Italian region and investigates potential issues of diagnosis and management during this period.