Dirty cattle have been commonly recorded in official animal welfare inspections in Sweden for years. The relevant authorities have initiated work to better understand the causes of dirty cattle, in order to improve compliance and standardize the grounds for categorizing a farm as non-compliant with welfare legislation when dirty animals are present. This study investigated the occurrence of dirty cattle in official animal welfare controls, on Swedish cattle farms, and examined farmers’ views on the reasons for non-compliance and on key factors in keeping animals clean. The data used were collected by animal welfare inspectors at the county level during the regular official inspections of 371 dairy and beef cattle farms over two weeks in winter 2020. In addition to completing the usual inspection protocol, the inspectors asked farmers a set of questions relating to why their animals were clean or dirty. Dirty cattle were found on 49% of the farms inspected, but only 33% of the farms were categorized as being non-compliant with Swedish welfare legislation. According to inspectors and farmers, dirtiness in cattle depends mainly on management routines, which is a promising result since routines can be improved. The results also revealed a need for better guidance for inspectors and farmers on when dirtiness should be categorized as non-compliance with animal welfare legislation.