To determine the consequences of disregarding first-degree relatives with psoriasis (FRP) as a classification criterion in juvenile idiopathic arthritis (JIA).
Criteria were examined in children from a prospective cohort with unclassified and psoriatic JIA.
FRP was the most common reason children were unclassified (57/85, 67%); all 57 children could be classified if FRP were disregarded as an exclusion criterion. FRP was a necessary inclusion criterion to classify 11/77 (14.3%) children with psoriatic JIA.
Eliminating FRP as an exclusion criterion, but keeping it as an inclusion criterion in psoriatic JIA simplifies classification, though it is unclear whether the resulting classification would be better.