Secondary restless legs syndrome is now considered one of the most common disorders you have never heard of. With a prevalence of around 5 to 15%, this disorder affects a significant portion of the population and therefore requires attention. The objective of this review was to look at all of the possible secondary causes of restless legs syndrome and whether there is strong enough evidence to support these associations. It is now widely accepted that the first depiction of possible RLS was outlined in 1672 by the well-known English Physician Sir Thomas Willis. Restless legs syndrome diagnoses has to meet the criteria set out by the international restless legs syndrome study group (IRLSSG). Restless legs syndrome can present in many various forms and can occur at any time throughout life. Patients who suffer from restless legs syndrome will often experience motor and sensory symptoms, or one of the two components. There are also other associated features such as sleep disturbances and fatigue, that can often negatively affect the quality of life of the sufferer. Restless legs syndrome can be treated with various nonpharmacological and pharmacological options. In this review we found a strong association between restless legs syndrome and iron deficiency, renal disease and pregnancy. Parkinson’s disease, essential tremor, some neuropathies and familial ataxias also showed some strong evidence towards an increase in the prevalence of restless legs syndrome in these disorders, however more long-term studies need to be done. We looked at many other possible associations, such as multiple sclerosis, myelinopathy, fibromyalgia and stroke. These, however, lack concrete findings to their associations, with possible alternative factors contributing to these associations with restless legs syndrome. It is important that restless legs syndrome sufferers be identified. Patients with mild symptoms, might simply need reassurance, while more moderate to severe symptoms might need pharmacological treatment. It is imperative that these secondary causes be screened when making the diagnosis of restless legs syndrome, as by treating them the symptoms of restless legs syndrome may be resolved and therefore not require other treatment modalities specific to restless legs syndrome.