Background: The role of allergy as risk factor for Long-COVID (LC) is unclear. We aimed to systematically review and appraise the epidemiological evidence on allergic diseases as risk factors for LC (PROSPERO: CRD42023391245). Methods: We examined literature for prospective cohort studies with a follow-up duration of 12 months for LC symptoms, published within the timeframe from January 2020 and January 2023 that recruited individuals with confirmed SARS-CoV-2 infection and information on pre-existing allergic diseases. Risk of bias and certainty of evidence were assessed (GRADE). Random effects meta-analyses were used to pool unadjusted ORs within homogeneous data subsets. Results: We identified 13 studies (participants range = 39 - 1,950), all of which were associated with high risk of bias. Four of these studies did not provide data to calculate ORs. Significant associations were observed between increased LC incidences and pre-existing asthma measured in hospital-based populations ( n = 6) and pre-existing rhinitis ( n = 3) ( OR = 1.94; 95% CI [1.08, 3.50]; OR = 1.96; 95% CI [1.61, 2.39]), respectively. However, the level of certainty regarding these exposure outcome associations was very low. Conclusion: Findings show that allergies may increase the risk of LC, although the reliability of this evidence is tenuous.