Research and reviews have resulted in clear indications for scleral lens (SL) wear. Those indications include visual rehabilitation; therapeutic use in managing ocular surface diseases, lid and orbit disorders; and refractive correction to enhance visual quality, comfort and quality of life. In some cases, the use of SLs may be contraindicated: the presence of low endothelial cell density; Fuchs' endothelial corneal dystrophy; glaucoma (because of the risk of an increase in intraocular pressure and the existence and location of draining devices and blebs); or overnight wear. While the literature provides an extensive description of the indications for scleral lens wear, the authors recognize that there is no paper reporting the contraindications to their use. The aim of this review is to illustrate the conditions for which SL wear is potentially contraindicated or requires caution. Improved knowledge of SL limits should reduce the risk of adverse events and increase the likelihood of fitting success.