Patients with monoclonal gammopathies comprise a heterogenous group. The few studies on incidence and follow-up are single-centre-based and may reflect referral bias. To avoid this, all patients (n = 1275) in mid-western Netherlands with a newly discovered paraproteinaemia in 1991, 1992 and 1993 were included in a population-based registry and divided into four major diagnostic groups: multiple myeloma and plasmacytoma (n = 230, 18%), other haematological diseases (n = 141, 11%), paraprotein-related internal diseases (n = 191, 15%) and monoclonal gammopathy of undetermined significance (MGUS, n = 713, 56%). To avoid a possibly erroneous diagnosis, patients who were classified as having MGUS but who did not undergo confirmatory bone marrow examination were included in a separate group ‘provisional MGUS’ (n = 524, 41%), whereas patients who did were classified as having ‘definite MGUS’ (n = 189, 15%). The ‘provisional MGUS’ patients were relatively older and had more often a poor performance status, but differences between this and the ‘definite MGUS’ group were otherwise small. Patients complaining of general malaise more often had a full work-up of their paraproteinaemia. Bone pain, hypercalcaemia, high total protein, and high ESR occurred predominantly in the myeloma group, whereas fever or infection was less often seen in these patients. This registry of patients with paraproteinaemias provided valuable data related to all different diseases associated with paraproteinaemia.