Extramedullary plasmacytomas constitute a rare and not well studied subset of multiple myeloma (MM) relapses. We report the incidence, clinical-laboratory features and outcome of patients with MM and extramedullary relapse (ExMeR). A total of 303 patients with symptomatic MM were recorded in a 13-year period in two institutions. Twenty-eight cases of ExMeR (9%) were recorded. There was an increased frequency of elevated lactate dehydrogenase (LDH) (p = 0.026), bone plasmacytomas (p = 0.001) and fractures (p = 0.002) at diagnosis, in patients with ExMeR compared to the others. ExMeR was associated with an ominous outcome, high LDH, constitutional symptoms and a statistically significant decrease of monoclonal paraprotein compared to levels at diagnosis (p = 0.009). Prior treatment with bortezomib was associated with a decreased hazard of ExMeR (p = 0.041). Overall survival (OS) was decreased in patients with ExMeR compared to the others (38 vs. 59 months, p = 0.006). Patients with MM with ExMeR have a lower OS and their clinical and laboratory features differ from those without.