ABSTRACT Oligo‐secretory and non‐secretory MM present a clinical challenge due to the difficulties in initial diagnosis, response to treatment assessment, and relapse detection. They are excluded from most clinical trials, which typically require measurable disease. We describe the characteristics and outcomes of 86 patients with secretory myeloma at diagnosis who developed an OSR, matched 1:1 to a cohort with secretory relapse (SR). With a median follow‐up of 9.3 years, 16.6% (48/289) of evaluable patients developed an OSR. Lower levels of light chains at presentation, and younger age are predictive of an OSR. The median OS since relapse of the OSR group was 4.01 (95% CI 1.625–6.395) versus 3.25 (95% CI 2.255–4.245) years in the SR control group ( p = 0.4). A third of our OSR cohort had a subsequent SR. We did not find any predictive factor for SR after OSR. The median OS of the subgroup of patients who developed a SR after OSR was 3.35 years (95% CI 1.541–5.159), versus 5.8 years (95% CI 2.072–9.528) in the group that remained oligo‐secretory ( p = 0.336). The median TTNT of the SR after OSR group was 1.68 years (95% CI 0.341–0.919) versus 4.58 (95% CI not reached‐not reached) in the group that remained oligo‐secretory ( p < 0.001).