Background: Börjeson-Forssman-Lehmann syndrome (BFLS; MIM 301900) is an infrequently described X linked disorder caused by mutations in PHF6, a novel zinc finger gene of unknown function. Objective: To present the results of mutation screening in individuals referred for PHF6 testing and discuss the value of prior X-inactivation testing in the mothers of these individuals. Results: 25 unrelated individuals were screened (24 male, one female). Five PHF6 mutations were detected, two of which (c.940A→G and c.27_28insA) were novel. One of these new mutations, c.27_28insA, was identified in a female BFLS patient. This was shown to be a de novo mutation arising on the paternal chromosome. This is the first report of a clinically diagnosed BFLS female with a confirmed PHF6 mutation. In addition, the X-inactivation status of the mothers of 19 males with suggested clinical diagnosis of BFLS was determined. Skewed (⩾70%) X-inactivation was present in five mothers, three of whom had sons in whom a PHF6 mutation was detected. The mutation positive female also showed skewing. Conclusions: The results indicate that the success of PHF6 screening in males suspected of having BFLS is markedly increased if there is a positive family history and/or skewed X-inactivation is found in the mother.