White populations in Australia and England share many genetic and phenotypic characteristics due to common ancestry, but Australians experience far higher rates of melanoma due to higher ambient ultraviolet radiation (UVR) levels. To gain insight into the role of UVR on melanoma development early in life, we used national cancer registration data and compared recent incidence rates and long-term trends of primary invasive cutaneous melanoma in Australian and English youth aged 0-24 years diagnosed 1990-2010. Incidence rates and standardized rate ratios (SRRs) with 95% confidence intervals (CIs) for 2006-2010 were calculated and incidence trends across the whole period were examined using JoinPoint regression. In Australian youth, overall melanoma incidence was double that in English youth (2.2 and 1.1 per 100,000, respectively). While melanoma rates were similarly rare among children <10 years in both countries, in subsequent 5-year age groups, incidence was significantly higher in Australia compared to England. Melanoma incidence among 15-24 year olds significantly increased by more than 2% per year in both sexes in England. However, after an initial non-significant increase, Australian rates for this older age group significantly decreased by 6.0% (95% CI, -8.2 to -3.8) per year in females from 1997 and decreased by 12.4% (95% CI, -20.3 to -3.8) per year in males from 2004. Long-standing primary prevention strategies targeted at curbing UVR exposure appear to have been effective in mitigating incidence trends in Australian youth, but decreases in incidence in English youth are yet to be observed.