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Background There is considerable international interest in understanding the sequential progression of multiple allergic conditions (also sometimes known as ‘the allergic march’). Objectives To study the sequential progression of multiple allergic conditions in a national birth cohort throughout childhood. Methods We constructed a birth cohort of 43 477 children born in 1990 and registered in UK general practices within a year of birth, using the national General Practice Research Database. Of these, 24 112 with complete follow-up until the age of 18 years were studied in order to understand disease progression and to estimate the absolute and relative risks of developing second and third allergic diagnoses following an index allergic condition. Results 52.1% of children were diagnosed with at least one condition at some point in childhood. We were able to describe 15 different disease trajectories. Eczema was the most likely index condition with 60.7% [95% confidence interval (CI): 59.8–61.6] of allergy sufferers being diagnosed with this condition first. For those with a diagnosis of eczema, the relative risks of being diagnosed with asthma followed by rhinitis and rhinitis followed by asthma were 1.59 (95% CI: 1.32–1.91; P<0.0001) and 0.54 (95% CI: 0.43–0.68; P<0.0001), respectively. For those diagnosed with asthma first, the relative risks of being diagnosed with eczema followed by rhinitis and rhinitis followed by eczema were 1.27 (95% CI: 0.96–1.68; P=0.095) and 0.27 (95% CI: 0.20–0.36; P<0.0001), respectively. For those diagnosed with rhinitis first, the relative risks of being diagnosed with eczema followed by asthma and asthma followed by eczema were 0.64 (95% CI: 0.42–0.95; P=0.025) and 0.47 (95% CI: 0.32–0.67; P<0.0001), respectively. Conclusions Among children diagnosed with multiple allergic diseases there is likely to be a number of variants of ‘the allergic march’. Of these, the diagnosis of eczema followed by asthma, which is in turn followed by rhinitis, is the most common trajectory. Surprisingly, some diagnoses indicate a possible strong protective effect of manifesting further likely allergic diagnoses. [ABSTRACT FROM AUTHOR]