The incidence of malignant melanoma has increased markedly among white populations in the recent decades. This may suggest that the incidence of melanoma in situ (MIS), the precursor of malignant melanoma, has also increased; however, few studies have assessed the incidence of MIS drawing on large population-based data sets. The present study aimed to assess MIS incidence trends in Denmark from 1997 to 2011. Data on MIS overall and on the histological subtypes superficial spreading MIS (SSM) and lentigo maligna (LM) were obtained from the Danish Nationwide Registry of Pathology. We calculated overall and age-specific incidence rates for both sexes, age-adjusted according to the world standard population. The average annual percentage change (AAPC) and 95% confidence intervals were calculated using log-linear Poisson models. Among both sexes, a high continued increase in MIS incidence rates overall and in that of the histological subtypes SSM and LM were observed during the period from 1997 to 2011. During this period, the age-adjusted MIS incidence rate increased from 2.6 to 8.1 cases among women and from 1.4 to 5.6 cases among men per 100 000 person-years. For both sexes, the highest AAPC in MIS incidence was observed during the most recent 5-year calendar period. A markedly higher AAPC was observed for SSM than for LM during the most recent 5-year calendar period for both sexes. The marked increase in incidence of MIS during the last 5 years of the period may indicate a growing awareness of skin cancer among the general Danish population and more frequent excision of suspicious skin lesions.