The identification and prompt diagnosis of Horner syndrome (HS) is essential for preventing permanent damage. HS may arise when a lesion presents anywhere along the three-neuron oculosympathetic pathway that begins at the posterior-lateral nuclei of the hypothalamus all the way through to the orbit. We present four cases and review the literature to familiarize the reader with the identification, diagnosis and treatment of Horner syndrome. The four patients, three adults and one child, were followed for at least 6 months following the initial diagnosis (range 6–18 months). There was partial resolution in three of the four cases, while the fourth resolved completely. There are numerous causes of HS, some of them iatrogenic. While iatrogenic cases of HR are rare in both adults and children, HS is seen more often following surgical procedures. Prompt recognition of the syndrome and correction of the offending agent may prevent permanent damage to the neuronal pathway. It is therefore recommended that practitioners be aware of the risks for development of iatrogenic HS and the signs for early detection.