Background: Metabolic syndrome (MetS) is a common comorbidity associated with hypertension that occurs more often in primary aldosteronism (PA). Our work aims to investigate the prevalence of MetS and its determinants in unilateral PA and bilateral PA, as confirmed by adrenal venous sampling (AVS). Methods: This was a retrospective, cross-sectional study. We investigated metabolic indicators in 160 cases of PA, categorized by AVS—82 with unilateral PA and 78 with bilateral PA. A control group of 80 non-PA patients with essential hypertension, matched for age and sex, was also included. Results: Unilateral PA had a higher aldosterone–renin ratio and lower serum potassium levels than bilateral PA. Nevertheless, bilateral PA exhibited a higher prevalence of MetS (41% vs. 30.5%; p = 0.001), obesity, BMI, LDL hypercholesterolemia, and hypertriglyceridemia than unilateral PA. Conclusions: Bilateral PA presents a greater incidence of MetS than unilateral PA, in spite of the latter showing a higher aldosterone–renin ratio and lower serum potassium levels. The results suggest that the mechanisms underlying MetS may differ between unilateral and bilateral PA.