Cystic fibrosis is a complex but common inherited condition resulting from abnormalities in the gene that code for the cystic fibrosis transmembrane conductance regulator. The clinical picture is variable, but usually includes symptoms from injury to the primary organs involved (exocrine pancreas, lung, sinus, liver, intestine) as well as an array of secondary complications.1 Recently we have experienced three cases of cystic fibrosis occurring in the setting of other rare conditions – Jervell Lange Neilson, pyridoxine dependent seizures and ataxia telangiectasia. Each of these obscured the symptoms and hence led to a delay in the diagnosis. One of the cases involved a child with a normal sweat test but genetic confirmation of cystic fibrosis. By describing these cases we hope that practitioners will consider a diagnosis of cystic fibrosis even when faced with other conditions which could contribute to the symptoms.