Using dynamic panel estimators, this article shows rejection of Gibrat's law for Portuguese companies in the service sector. In companies as a whole, we find that growth depends positively on growth in the previous period and on debt, and depends negatively on size. When we subdivide the sample into small- and medium-sized companies and large companies, the results are similar to those obtained when we take companies as a whole. The differences concern the relationship between ownership control and growth, which is positive in the case of small- and medium-sized companies, and the non-influence of growth in the previous period on growth in the current period in the case of large companies.