Monoclonal gammopathy of undetermined significance (MGUS) is rare in young patients (age <40 years at diagnosis), with a prevalence of <0.3%, representing ~2% of all patients with MGUS. We hypothesized that MGUS detected in young patients may be associated with a higher risk of progression. We examined 249 patients with MGUS < 40 years old. Among these, 135 patients had immune-related conditions, including infections, autoimmune and inflammatory disorders at the time of diagnosis of MGUS. The risk of progression to multiple myeloma or a related disorder at 5 years and 10 years was 6.0% and 13.8%, respectively. The size of M protein was a significant risk factor for progression (HR 4.2, 95% CI 2.2-7.9). There was a trend that the risk of progression was higher in patients without immune-related conditions (HR 2.36, 95% CI 0.85-6.52, p = 0.088). The M protein resolved in 36 (14%) patients, with a greater likelihood of resolution in patients with immune-related conditions (RR 1.9, 95% CI 1.02-3.6). Young patients with MGUS have a similar risk of progression as older patients, 1.4% per year. Over 50% are diagnosed in the setting of immune-related disorders. Patients with immune-related disorders may have a lower risk of progression.