Creation of duplicate account or contact on Lead conversion

Upon converting a Lead, Salesforce will create an Account, Contact and a choice of having an Opportunity created as well. If a duplicate Account exists in Salesforce, the system will prompt you with the following choices.
 

1. Create a New Account.
2. Attach to the Existing Account.

If you choose to create a new Account, you will create a duplicate Account with the new Lead. Choosing to attach the Lead to the existing Account will create a new Contact on the existing Account.

Note: If there are more than 3 to 5 similar Account name in the org the existing Account might not list all the Accounts. The only way to check the Account names would be to create a report on Accounts. For more, please review Build a Report in Salesforce Classic.


See also:
Considerations for Converting Leads