In several cancer registration areas, the trends in the incidence and mortality of multiple myeloma (MM) have been rising over the last few decades. Pedigrees studies on families with multiple affected members have supported the hypothesis of a contributing hereditary etiology of MM due to shared genetic factors. The aim of our study was twofold: 1) to assess incidence trends of MM over the period 1961-2003 using national cancer registry data and; 2) to quantify the familial risk of MM using the 2004 update of the Swedish Family-Cancer Database. For men, the age-standardized rates were 4.33 per 100,000 in 1961-65 and 4.79 in 2001-03. The corresponding rates for women were 2.76 and 3.43. In the elderly, MM rates have risen from 28.7 per 100,000 to 36.2 in men, and from 20.2 to 24.5 in women. MM clustered in families with MM (standardized incidence ratio, SIR=2.45), non-Hodgkin lymphoma (SIR=1.34) and chronic lymphocytic leukaemia (SIR=2.45). No association was found for Hodgkin lymphoma and other leukaemias. Significant associations were found for rectal, stomach, cervical, prostate, bladder, endocrine glands and connective tissue malignancies. Our study adds further evidence that the incidence of MM in Sweden has been constant for several decades. The apparent increase observed in the elderly is, at least in part, attributable to improved diagnostics and certification. MM aggregates in families with MM, chronic lymphocytic leukaemia and, to a lesser extent, with non-Hodgkin lymphoma. If environmental factors can be excluded, the pattern of familial risk of MM is consistent with an autosomal dominant mode of inheritance.