You want to use the Initialize event for the userform.
The code would be something like this:

Private Sub UserForm_Initialize()
TextBox1.Text = Worksheets("Sheet1").Range("A1").Value
End Sub

You will need to use the actual names for your textbox and
worksheet.
-----Original Message-----
Dear VBA Experts,

I have a UserForm where I want to have a textbox
populated
with an amount in a cell. I have tried the ControlSource
= the cell or the Value = the cell and am getting an
error
message. Assuming I have a number in cell A1, what is
the
code to have that info populate a textbox in a userform
so
that when the userform is opened, the textbox already
shows that amount? Thanks in advance.

Neal
.