This work was a follow-up study (birth years 1999-2003) of the prevalence of autism in children of Somali background living in the county of Stockholm, Sweden. In a previous study (birth years 1988-98), the prevalence of autism associated with learning disability was found to be three to four times higher among Somali children compared with other ethnicities in Stockholm. We examined all records of children of Somali background, born from 1999 to 2003, registered at the centre for schoolchildren with autism and learning disability. The census day was 31 December 2009. The prevalence of autism and PDDNOS (with learning disability) was 0.98% (18/1836) in the Somali group and 0.21% (232/111 555) in the group of children of non-Somali origin (p less than 0.001). The increased prevalence remained and was now between four and five times higher in children of Somali background. A clinical observation was that more than 80%, in addition to autism and learning disability, had a profound hyperactivity. The findings accord with many other studies reporting higher prevalence rates of autism in children of immigrant mothers. We discuss the need for further research of underlying mechanisms.