The serious drug and drug smuggling offenders active in Stockholm are linked by means of co-offending to other persons in large criminal networks. Within these networks, the individuals have large numbers of superficial and transient contacts with one another. It appears to be particularly important to have contacts with other drug offenders throughout Sweden, and particularly in the Skåne region. The majority of the convicted drug offenders have a Nordic background. The study indicates that dealers in the Stockholm area know drug smugglers in Sweden's metropolitan areas. In their turn, the drug smugglers in the metropolitan areas have contacts with persons involved in the smuggling of other goods primarily in the county of Skåne. A large proportion of the persons included in the data set were suspected of committing drug offences and appear to be focused to some extent on drug offending and on offences involving one or two illicit substances. They also engage in other types of criminal activity to a large extent, however, and are thus not exclusively specialised in drug offending. Persons involved in serious drug crime, including drug smuggling, are often males in their thirties. These individuals often choose other males as co-offenders. It is generally common to commit drug offences together with co-offenders and the most criminally active individuals are also those with the largest numbers of co-offenders. The co-offending partnerships that commit drug offences are not particularly durable over time, however, and it is unusual for drug offenders to restrict themselves to committing offences with one and the same co-offender.