Prior research has indicated that children with autism spectrum disorders (ASD) or attention disorders (AD/HD and DAMP) are at risk for written language difficulties. But existing research is limited, especially so for ASD. The psycholinguistic basis of the connection between ASD and attention disorders, on the one hand, and written language difficulties, on the other, is furthermore not well understood. The aim of the thesis was to investigate abilities in reading comprehension, word decoding and spelling in relation to questions raised in prior research. In study 1, 77 children between 7 – 14 years participated: 37 children with ASD, 21 children with DAMP, and 19 children in the comparison group. The three groups were matched for mental age. In study 2 only girls participated: 20 with ASD, 36 with AD/HD and 54 comparison girls, with an age range of 8-17 years. Results from the two studies indicated that the written language ability differed depending on whether word decoding, spelling or reading comprehension was considered. In study 1 the only significant difference was between the children with ASD and the comparison group in reading comprehension, with a lower performance by the children with ASD. In study 2, a continuous measure of autistic symptomatology related negatively only to reading comprehension, while AD/HD symptomatology was negatively related to spelling, word decoding and to reading comprehension. In regression analyses both autistic- and AD/HD symptomatology explained significant proportions of variance in reading comprehension after the influence of oral vocabulary, word decoding and nonverbal ability was controlled for. The results from the two studies do not merge into a completely coherent whole, but are partly in line with previous suggestions of more global written language difficulties in children with attention disorders, while children with ASD have more specific difficulties in reading comprehension. Directions for future research and preliminary implications for educational practise are discussed.