This paper presents a model to minimise inventory and setup costs in a multi-product operation where production is organised in campaigns. A campaign is defined as a number of successive, equally sized lots of a same product. Major and minor sets are considered. The decision variables are the per product time between campaigns and number of lots per campaign. Two cases are presented: when the time between campaigns is common to all products, and when it is a multiple of a common period. Examples are presented which demonstrate the cost differences based on the assumption of time between campaigns.