Incidence rates of Multiple myeloma and immunoproliferative diseases (MM) are higher in men than in women, possibly due to differences in circulating sex hormones over the course of a lifetime. Only a few studies have investigated MM risk in relation to reproductive factors; while two studies with small numbers of MM cases found no association, a recent study found reduced MM risk among women with four or more children compared to those with only one child. In the planned investigation, NCI investigators will evaluate the relations between reproductive factors and MM risk by pooling data across case-control studies participating in the International Multiple myeloma and immunoproliferative diseases Consortium.  Data on reproductive factors and other selected covariates (e.g., BMI, alcohol, race, and smoking) will be harmonized across studies, and odds ratios and 95% confidence intervals will be estimated using logistic regression. Statistical analyses will be led by collaborators at the Catalan Institute of Oncology in Spain.