AIMS:Comorbidities are common at diabetes onset and may influence long-term outcomes. We examined national trends in the prevalence, number, and multimorbidity patterns among U.S. adults with newly ascertained diabetes, distinguishing concordant metabolic risk factors, concordant vascular diseases, and discordant conditions. METHODS:We analyzed National Health and Nutrition Examination Survey data (1999-August 2023) for adults (≥20 years) with newly ascertained diabetes (diagnosed at the survey or ≤2 years prior; n = 4,243). Age-adjusted prevalence of 13 comorbidities, mean comorbidity count, and multimorbidity patterns were estimated across three periods. Trends were assessed using logistic and linear regression and pattern distributions using chi-square tests. RESULTS:Obesity increased from 58.3% (1999-2006) to 71.0% (2015-2023) (p = 0.0003); Chronic lung disease rose from 15.4% to 22.8% (p = 0.007). Chronic kidney disease (∼30%) and cardiovascular disease (11.8%-14.1%) were stable. Arthritis (∼40%), sleep disorders (29.2%-38.5%), and dental caries (∼30%) were common but stable. The mean comorbidity count increased from 4.25 to 4.51 (p = 0.038), with greater overlap of concordant and discordant conditions (p = 0.008). CONCLUSIONS:From 1999 to 2023, obesity, chronic lung disease, and total number of comorbidities increased among adults with new diabetes. Multimorbidity patterns increasingly encompassed both concordant and discordant conditions, potentially complicating management and worsening outcomes.