This study aimed to investigate the prevalence of previously undocumented suspected diagnoses identified during preventive health examinations in middle-aged adults, and to examine their associations with clinical and behavioral factors. In this cross-sectional study, 1,040 adults aged 45-59 years underwent preventive clinical examinations comprising self-reported medical histories, anamneses, previous medical records, and laboratory tests (LDL cholesterol, blood pressure, HbA1c, TSH). Suspected diagnoses were defined by clinical thresholds (e.g., LDL > 116 mg/dl, hypertension ≥ 140/90 mmHg, HbA1c > 6.0%). Multivariable logistic regression analyzed associations between multiple variables and the three binary outcomes, any suspected diagnosis of hypertension and elevated cholesterol. The mean age of participants was 52.93 years (sd = 4.17), with 61% male (n = 631). In total, 421 (41%) had at least one newly identified suspected diagnosis. The most frequent findings were elevated LDL cholesterol (n = 287, 28%) and hypertension (n = 93, 9%). Male sex was associated with higher odds of any suspected diagnosis (OR: 1.42; 95%-CI: 1.09-1.85) and having hypertension (OR: 2.24; 95%-CI: 1.31-3.99). BMI was associated with hypertension (OR: 1.15; 95%-CI: 1.08-1.21) and showed a weak association with elevated cholesterol (OR: 1.04; 95%-CI: 1.00-1.08). A recent blood test was linked to lower odds of any suspected findings (OR: 0.65; 95%-CI: 0.50-0.84). No consistent associations were observed for lifestyle factors. A family history of dyslipidemia was associated with elevated cholesterol (OR: 1.55; 95%-CI: 1.01-2.40). Preventive health screenings can reveal a substantial number of previously undiagnosed conditions, particularly among individuals with limited healthcare contact or elevated risk. The findings suggest that such screenings may offer a significant value for targeted risk groups in midlife. Further research should evaluate long-term outcomes and cost-effectiveness.