Visual loss with dancing extremities and mental disturbances. A case is reported of a teenage girl, who presented with a profound loss of vision in the right eye, secondary to retinal vasculitis. During the preceding year, a gradual change in her personality had been noted, associated with a deterioration in her intellect. She developed an area of pigment epithelial disturbance in the macular region of the right eye, and subsequently, optic atrophy. One year after this, she had a similar, but more localized episode in the left eye. She later developed involuntary movements, and two years after initial presentation, a diagnosis of subacute sclerosing panencephalitis was made. Subsequently her clinical condition deteriorated rapidly and she died. Post-mortem examination confirmed the diagnosis of subacute sclerosing panencephalitis. This case demonstrates the insidious nature of the disease and suggests that the diagnosis of subacute sclerosing panencephalitis should be considered in any child or young adult who presents with unexplained retinal vasculitis, maculopathy or chorioretinitis. 